THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 


GIFT 

of 
iltcs.  Clifford  B.  Walker 


^V/^ 


l^Ad'it*— 


Parveblirdhed  -  Fartaenblindheit  -  Colour-blindness. 

Cecite  des  couleurs-Cecita  di  ^.olore. 


Explanation  of  this  Plate  will  be  found  on  page  XIX. 


'  ^^-'^ 


I 


CoJrr  BJindness 


lla 


6  7 

II 


fled  nJindi. 


Less 


to  // 

II 

/led  JjJin  dness. 


9 

I 


GrecJi  B/uidn 


less. 


12 


II 

Green  /JJindness. 


'///j.strate  /Jw  m  et/iad o/'h'.st^Jif/^  and  fAe  mistcdes  oflJi,:  aJorA 


COLOR-BLINDNESS : 


ITS  DANGERS   AND   ITS  DETECTION, 


BY 

B.  JOY  JEFFRIES,  A.M.,  M.D., 

(HABVAEB,) 

Fellow  of  the  Massachusetts  Medical  Society;  OPj^^halmic  Surg^^on    Mas^^^^^^^^ 
Charitable  Eye  and  Ear  Infirmary,  Carney  Hospital,  and  ^ew-England  Hospital 
"^lo  W  nfenandChildren;  MeniberofthelnteniaU^ 

Ophthalmology,  American  Ophthalmological  Society,  Boston  Society 

of  MedicaF  Sciences,  Boston  Society  for  Medical  Observation. 

Boston  Society  of  Natural  History,  &c. 


BOSTON : 
HOUGHTON,  OSGOOD   AND   COMPANY. 

©be  EitierfiiUe  Press,  CamtrUise. 

1880. 


Copyright,  1879, 
By  B.  joy  JEFFRIES. 

All  rights  reserved. 


C.  y.  Peters  &>  Son,  Stereotypers, 
73  Federal  Street. 


Biomedical 
Library 

W  vV 
1^11 


TO 


FRITHIOF   HOLMGREN,  M.D., 

PEOFESSOK  OF  PHTSIOLOGT  IX   THE   TJNTVEKSITY  OF 
ITPSALA,   SWEDEN, 


THIS    VOLUME 


IS  BESPECTFULLY  DEDICATED. 


'Why  should  we  look  one  common  faith  to  find, 
Where  one  in  every  score  is  color-blind? 
If  here  on  earth  they  know  not  red  from  green, 
Will  they  see  better  into  things  unseen?" 

Dr.  O.  W.  Holmes  :  Andover  Poem,  June,  1878. 


COI^TENTS. 


PREFACE vii-xiii 

INTRODUCTION xv-xvi 


CHAPTER 

I.  HisTOEicAL  Cases  of  CoLOH-BLrNDNESS    .  1-6 

n.  Colok-Blixd  Mistakes         ....         7-21 

ni.  FoKMEPv  Classification  of  the  Colok-Blind  22-25 

lY.  Present  Classification  of  the  Colok-Blind 

IN  ACCOKDANCE  WITH  THE  ToUNG-HeLMHOLTZ 

Theory  of  Color-Pekception       .        .        26-41 
Y.    Precise  Condition  of  the  Yision  of  the  Col- 

or-Blind 42-47 

YI.    Color-Blindness  from  Disease  or  Injury,      48-53 
YII.    Color-Blindness  Hereditary    .        .        .        54-63 
Yin.    Physical    Peculiarities    connected   with 

Color-Blindness 64-68 

IX.    Frequency  of  Color-Blindness  in  Males,       69-79 
X.    Infrequency   of   Color-Blindness   in  Fe- 
males          80-87 

XI.    Concealment  of  Color-Blindness  in  Practi- 
cal Life 88-110 

xn.  Incurarility  of  Congenital  Color-Blind- 
ness          111-124 

XIII.  Palliation  of  Congenital  Color-Blind- 
ness          125-136 

XIY.  Dangers  arising  from  Color-Blindness  on 
Railroads.  —  Condition  of  Color -Blind 
EiiPLOYES 137-160 

V 


VI  CONTEKTS. 

CHAPTEB  PAGE 

XY.    Dangers   feom    Color  -  Blindness   on   the 

Ocean 161-165 

XVI.    Can  the  Eaileoad   and   Marine   Signals 

BE   CHANGED  ? 166-175 

XYII.    Necessity  and  Difficulty  of  Control,    176-181 
XYIII.    Methods    of    Testing    for    Color -Blind- 
ness .        .        .      ■ 182-195 

XIX.    Holmgren's  Method  of  detecting  Color- 
blindness, AS  described  in  his  Original 
Work.— Examination  and  Diagnosis,    196-220 
XX.    Special    Directions    for    conducting   the 

Test 221-236 

XXI.    Efforts  to  conceal  or   to   feign   Color- 
blindness            237-240 

XXII.  Method  of  deciding  the  Precise  Amount 
OF  Color-Blindness  by  Professor  Holm- 
gren's Chromatoskiameter,  or  Color- 
Sense  Tester. — Professor  Donders's 
Method   of   determining  Quantitative 

Color-Perception 241-250 

XXIII.    Laws  of  Control  of  Color-Blindness  now 
IN  Force  in  Europe. — Legislative  Ac- 
tion OF  THE  State  of  Massachusetts,  251-280 
XXI Y.    Personal   Experience    with    Holmgren's 

Method.  —Suggestions  as  to  its  Use,  281-286 

XXY.    Conclusions  and  Kecapitulation        .    287-289 

BroLioGBAPHY 291-308 


PKEFACE. 


I  HAVE  dedicated  this  volume  to  my  friend  Professor 
Holmgren,  because  I  consider  that  to  him  above  all 
others  do  we  owe  the  present  and  future  control  of 
color-blindness  on  land  and  sea,  by  which  life  and 
property  are  safer,  and  the  risks  of  travelling  less. 

To  his  Majesty  the  King  of  Sweden  are  due  the 
thanks  of  all  for  his  personal  interest  in  the  investiga- 
tion of  color-blindness,  and  his  practical  good  sense  in 
immediately  putting  into  execution  the  plans  and  pro- 
posals of  Professor  Holmgren,  by  which  the  subject 
was  so  prominently  brought  forward  as  to  command  the 
attention  and  example  of  other  nations.  It  is  ear- 
nestly hoped  that  this  country  will  follow  rapid  suit. 

Professor  Holmgren's  book  on  ''Color-Blindness  and 
its  Relations  to  Railroads  and  the  Marine  "  was  pub- 
hshed  in  Swedish,  in  1877,  at  Upsala.  Immediately 
after  this  a  French  translation  was  printed,  which  soon 
called  very  general  attention  to  his  labors  and  their 
results.  An  authorized  translation  into  German  ap- 
peared last  year  (1878).  I  had  agreed  with  him  to 
translate  the  work  into  Enghsh,  when  an  abridged  trans- 
lation appeared  from  the  Reports  of  the  Smithsonian 


VIU  PREFACE. 

Institute  at  Washington.  This,  of  course,  prevented 
any  pubhsher  from  being  wilUng  to  risk  a  complete 
translation.  The  very  necessary  explanatory  colored 
plate  was  not  given  in  the  Smithsonian  translation.  I 
understand  that  it  will  be  in  an  extra  edition.  This 
EngUsh  translation  is  so  abridged  as  to  greatly  inter- 
fere with  its  value  and  its  practical  use. 

Had,  however,  I  been  enabled  to  reproduce  Professor 
Holmgren's  book  entire,  I  am  afraid  it  would  not  have 
accomplished  its  purpose  so  well  in  this  country  as  in 
Europe,  from  the  general  lower  tone  of  scientific  knowl- 
edge on  the  part  of  those  for  whom  it  was  especially 
written,  and  also  the  lack  of  just  the  persons  —  namely, 
the  railroad-surgeons — who  could  make  immediate  ap- 
plication' of  the  method  for  detecting  color-bUndness, 
and  have  convinced  the  authorities  of  its  necessity. 
Aside,  also,  from  the  diflSculties  of  publication,  I  found 
that  a  simple  translation  was  not  likely  to  be  so  gener- 
ally read. 

To  bring  before  the  community  the  dangers  and  the 
prevalence  of  color-bhndness,  I  thought  it  best  to 
prosecute  my  researches  amongst  the  places  of  learn- 
ing and  teaching.  Hence  I  chose  our  immediate  uni- 
versities, colleges,  and  public  schools.  Thus,  whilst  I 
was  pursuing  my  own  individual  studies  of  color-blind- 
ness, I  was  at  the  same  time  gathering  the  necessarj^  sta- 
tistics in  proof  of  the  position  I  took,  and  disseminating 
a  knowledge  of  the  whole  subject,  ver}^  especially  the 
important  one  of  its  frequency.  It  is  rather  curious 
that  this  volume  is  only  the  third  monogi'aph  in  book- 
form  on  this  subject.  Professor  Wilson  of  Edinburgh 
pubhshed  in  1855  a  small  book,  being  a  collection  of 
his  several  articles  on  this  subject.  Yet  the  literature 
of  normal  and  abnormal  chromatic  power  is  pretty  ex- 


PREFACE.  IX 

tensive,  as  ma}-  be  seen  bj  the  bibliography  appended 
to  this  volume.  I  first  publicl}-  discussed  the  subject 
before  the  Boston  Society  of  Natural  History,  March 
7,  1877.  An  article  of  mine  on  the  "Dangers  from 
Color-Blindness  in  Railroad  Emploj'es  and  Pilots  "  was 
printed  in  the  Ninth  Annual  Report  of  the  Massa- 
chusetts State  Board  of  Health,  1878.  April  8,  1878, 
I  gave  a  lecture  on  color-bhndness  before  the  Society 
of  Arts  of  the  Institute  of  Technologj-  in  Boston. 
Feb.  23,  1878,  I  read  a  paper  on  the  "  Incurabiht}'  of 
Congenital  Color-Bhndness ' '  before  the  Suffolk  Distiict 
Medical  Society-  in  Boston,  published  in  "  The  Boston 
Medical  and  Surgical  Journal"  March  28,  1878.  May 
25, 1878, 1  read  a  paper  on  the  "  Relative  Frequenc}-  of 
Color-BUndness  in  Males  and  Females  "  at  the  Suffolk 
District  Medical  Society,  and  also  at  the  Jul}'  meeting 
at  Newport  of  the  American  Ophthalmological  Society  ; 
published,  July  26,  in  "  The  Boston  Medical  and  Surgi- 
cal Journal."  The  substance  of  these  papers  is  in- 
cluded in  this  volume.  I  have  quoted  largely  from 
Professor  Wilson's  book,  not  only  because  it  is  quite 
out  of  print,  but  also  because  the  cases  he  relates  are 
interesting  as  being  in  England,  and  his  deductions  are 
truthful  and  valuable,  although  much  of  the  theory 
presented  is  now  old  to  science.  I  have  given  a  good 
part  of  Professor  Holmgi'en's  book,  including  what  is 
essential  to  be  known  and  understood  by  our  railroad 
authorities  and  the  speciahsts  they  must  employ  in 
carr}-ing  out  any  system  of  thorough  examinations. 
The  explanations  and  dii'ections  may  seem  to  many 
unnecessarily  minute,  and  the  description  too  extended  ; 
but  these  are  especially  intended  for  examiners,  who, 
I  think,  when  using  this  test,  will  thanli  me  for  putting 
them  within  their  easy  reach. 


X  PREFACE. 

The  importance  of  this  whole  question  of  color-blind- 
ness I  need  not  insist  on  here.  "The  Railroad  Ga- 
zette "  of  Jan.  24,  1879,  after  discussing  the  740  acci- 
dents by  which  204  people  were  killed  and  756  injured, 
says,  "  What  most  needs  doing  now  is  the  improve- 
ment of  the  men  who  work  the  roads,  —  officers  and 
employes,  —  though  there  is  still  plenty  of  room  for 
progress  in  the  tools  with  which  they  work.'' 

I  have  not  in  this  volume  entered  into  the  loss  of 
time  and  money  from  color-blindness  in  the  great  indus- 
tries where  a  perfect  chromatic  sense  is  needed  ;  or  the 
mortifications,  &c.,  arising  from  constant  mistakes  of 
dress  &c.,  in  every-day  life,  — as  all  these  bear  no  rela- 
tion to  the  importance  of  the  danger  to  life  and  prop- 
erty on  land  and  sea  from  this  curious  visual  defect. 
The  railroads  of  England  pay  two  milUon  dollars  a 
year  for  killed  and  injured  travellers. 

I  must  explain  some  expressions  in  my  text.  I 
alwaj^s  use  the  term  color-bhndness,  instead  of  Dalton- 
ism, as  more  truthfully  representing  the  defect  in  gen- 
eral, as  Dalton  was  red-blind  ;  and  also  in  order  not  to 
continue  to  attach  this  defect  to  his  name.  This  has 
become  pretty  universal,  except  with  the  French,  who, 
having  no  one  word  for  color-blindness,  still  say  Dal- 
tonisme  for  brevity's  sake.  My  speaking  of  a  color- 
blind I  would  apologize  for  by  sajdng,  were  I  to  have 
added  "  person  "  each  time,  my  readers  would,  I  think, 
have  preferred  the  present  bad  grammar. 

I  am  quite  aware,  that,  instead  of  presenting  the  ma- 
terial of  this  volume  in  its  present  shape,  I  could  have 
given  a  condensed  essay  on  color-blindness  more  easily 
read  ;  but  such  a  book  would  not  meet  the  wants  of  the 
immediate  future.  The  question  of  color-blindness  is 
soon  coming  up  in  a  very  practical  form  in  this  coun- 


PREFACE.  XI 

try.  Those  who  have  to  deal  with  it  will  properly  aak 
for  the  original  niaterlal  which  they  may  themselves 
study,  and  which  I  have  here  collected.  Such  material, 
as  my  bibhography  shows,  is  widely  scattered  and  in 
foreign  languages  ;  whilst  other  I  here  present  has  never 
been  iDublished.  For  this  reason  I  risk  the  natural  crit- 
icism mj^  work  will  call  forth,  rather  than  fail  to  give 
full  opportunity  for  those  who  from  their  position  must 
hereafter  have  m}^  gathered  material  within  then-  reach. 
As  this  volume  is  intended  to  meet  the  wants  of  sev- 
eral quite  different  classes  in  the  community,  its  con- 
tents are  somewhat  varied.  Many  of  the  chapters  may 
be  read  by  themselves,  by  those  who  are  onl}^  interested 
in  the  subject  from  the  point  of  view  touched  on  in  that 
special  chapter.  General  readers  will  find  the  histori- 
cal cases,  and  the  curious  mistakes  caused  bj'  this 
chromatic  defect,  of  most  interest  to  them  perhaps. 
Phj'sicians  wiU  be  interested  in  facts  relating  to  color- 
bhndness  from  disease,  its  heredit}^,  and  the  supposed 
pecuharities  heretofore  connected  with  it,  as  also  its  in- 
curabiht}'.  Scientists  and  ph3'siologists  will  naturally 
turn  to  the  accounts  of  the  precise  condition  of  color- 
blindness audits  relation  to  normal  color-sense,  as  well 
as  the  additional  methods  of  detection.  The  color-bUnd 
cannot  but  be  interested  in  the  palliatives  of  congenital 
color-bhndness,  since  we  can  now  do  more  for  them  than 
formerly.  The  dangers  on  land  and  sea  concern  us  all. 
Railroad  authorities  will  find  full  explanation  of  the 
precise  condition  of  their  color-blind  employes.  The 
possible  change  of  railroad  and  marine  signals  will  also 
concern  them  and  the  officers  of  the  navy  and  mercan- 
tile marine.  The  possibUity  of  detecting  and  eUminat- 
ing  the  color-blind  is  important  to  those  whose  position 
requires  them  to  avoid  employing  such.     The  methods 


Xll  PREFACE. 

of  so  doing  interest  the  specialists  employed  for  this 
purpose.  Our  national  and  state  legislatures  and  rail- 
road commissioners  will  naturally  turn  to  the  account 
of  the  present  provisional  European  laws  in  reference 
to  the  control  of  color-blindness  on  land  and  sea. 

I  have  hitherto  avoided  seeldng  for  the  color-bhnd, 
and  discouraged  those  who  I  understood  would  apply 
to  me  ;  because  I  desired  to  have  my  statistics  as  near 
as  possible  precisely  represent  the  truth  as  to  the  prev- 
alence of  this  chromatic  defect.  My  present  numbers 
are  so  large  as  to  perfectlj^  decide,  for  m3'self  at  least, 
this  point.  I  therefore  am  now  anxious  to  hear  from 
the  color-blind,  by  letter  or  otherwise,  as  each  and 
ever}^  account  is  of  value.  The  personal  observations 
of  any  who  have  this  defect  would  interest  me,  and  be 
of  service  to  science.  All  names  would  of  course  be 
strictly  confidential.  I  am  at  present  devoting  special 
attention  to  the  question  of  heredit}^,  and  naturall}^  very 
anxious  to  hear  from  an}''  one  on  this  point.  In  many 
color-blind  families  the  facts  must  be  pretty  well  known 
as  to  the  different  members,  and  such  I  desire  to  have 
causa  scientice.  My  professional  brethren  may  be  able 
to  assist  me  in  this,  and  I  would  hereby  ask  it  of  them. 
I  well  know  that  many  color-blind  persons,  whilst 
shrinlving  from  exhibiting  their  defect,  would  not  hesi- 
tate to  give  an  account  of  their  case  when  assured 
their  names  would  not  be  used. 

The  dedication  of  this  volume,  and  the  free  use  I 
have  made  of  his  material,  show  how  much  I  am  in- 
debted to  Professor  Holmgren  of  Upsala,  Sweden,  with 
whom  I  have  been  in  constant  communication.  I  have 
also  to  greatly  thanli  Professor  Bonders  of  Utrecht  for 
advice  and  suggestions,  as  well  as  for  the  rules  of  the 
Holland  railroads.     I  am  indebted  for  information  and 


PREFACE.  Xm 

numerous  publications  to  the  following  gentlemen, 
whom  I  would  hereby-  gi'atefull}^  remember :  Dr.  Mag- 
nus of  Breslau,  Drs.  Eulenberg  and  Hirschberg  of  Ber- 
hn,  Dr.  Stilling  of  Cassel,  Dr.  Cohn  of  Breslau,  Dr. 
Zehender  of  Rostock,  Dr.  Schiess  of  Basle,  Dr.  Warlo- 
mont  of  Brussels,  Professor  Delboeuf  of  Lille,  Drs. 
FaATC  and  Dor  of  Lyons,  Dr.  Nicati  of  Marseilles,  Dr. 
Quaglino  of  Pavia,  Dr.  Daae  of  Kragero,  Norway,  and 
Dr.  Hjort  of  Christiana,  Xorwa}',  Dr.  A.  von  Reuss 
of  Vienna,  Dr.  Robertson  of  Edinburgh,  and  IVIr.  S. 
Wright  Dunning  of  ' '  The  Railroad  Gazette  ' '  of  New 
York. 

To  the  Boston  School  Board  m}'  thanks  are  specially 
due  for  permission  to  test  the  scholars  of  the  public 
schools,  in  which  work  I  am  still  engaged. 

To  avoid  cumbering  this  volume  with  references,  I 
use  an  author's  name,  and  the  bibhograph}^  will  enable 
the  reader  to  turn  to  the  original.  There  is,  I  believe, 
no  excuse  for  a  writer  not  gi^'ing  his  best  work  to  the 
pubhc ;  but  I  must  add  here,  that  the  time  for  my 
eighteen  thousand  examinations  for  color-blindness, 
and  the  preparation  of  this  volume,  has  been  stolen 
from  the  busy  hours  of  a  professional  life. 


B.  Joy  Jeffries,  M.D. 


15  Chestnut  Stbeet,  Beacon  Hill,  Boston. 


INTRODUCTION. 


There  are  some  points  in  reference  to  color-percep- 
tion which  I  must  first  explain  to  my  unprofessional 
readers,  to  show  what  color-blindness  is  not.  Our 
point  of  best  \4sion  on  the  retina  is  directly  in  the 
centre,  and  over  but  a  smaU  space  here ;  so  that,  to 
see  an  object  distinctly,  we  must  carefully  turn  the  e3^e, 
to  keep  the  picture  on  this  portion.  In  looking  at  a 
long  word  on  a  page,  we  unconsciously  travel  along  it 
to  catch  all  the  letters.  If  we  keep  our  eye  fixed  on 
one  point,  and  move  a  letter  away  from  this  point,  its 
form  is  soon  lost,  and  we  fail  to  recognize  it.  In  other 
words,  if  the  image  of  the  letter  falls  on  the  retina  but 
a  little  way  from  the  centre,  called  "the  yellow  spot " 
fi'om  its  color,  it  is  confused.  Form-perception  dimin- 
ishes ver}^  rapidly  from  the  centre  outwards  in  all  direc- 
tions. Now,  this  is  also  the  case  in  reference  to  color. 
Let  one  e3'e  be  closed,  and  the  other  fixed  on  a  bright- 
red  object,  like  a  wafer,  held  before  it.  When  moved 
gi-aduall}^  out  from  the  central  field  of  vision,  the  wafer 
will  decrease  in  brightness,  and  finally  appear  black. 
Its /orm  we  may  still  discern.  This  is  not  color-blind- 
ness.    A  painter  has  added  a  bright  little  scarlet  flower 


XVI  INTEODUCTION. 

down  in  one  corner  of  his  picture,  and  turns  to  work  in 
the  centre,  when  suddenly  the  scarlet  flower  loses  its 
color,  because  its  image  falls  far  away  on  the  retina 
from  the  point  of  best  color-perception.  This  same 
will  be  found  in  reference  to  the  other  primary  colors 
in  varying  degrees. 

Another  point :  Whenever  the  retina  is  tired  out 
with  one  color,  it  can  onty  perceive  the  complementar}^ 
one.  If  with  one  eye  we  gaze  steadily  for  some  sec- 
onds at  a  bright-green  disk  on  a  white  ground,  and  then 
quickly  look  at  another  white  surface,  we  shall  see  a 
red  disk.  Gazing  fixedly  at  the  setting  sun  when  a 
deep  red,  and  turning  quickly  to  the  east,  we  shall  see 
a  rising  green  sun.  I  hardly  need  say  this  also  is  not 
color-blindness. 

Again  :  the  crystalhne  lens  in  the  eye  becomes,  with 
age,  harder,  and  of  a  yellowish  color,  —  up  to  positive 
blackness.  When  opaque,  it  prevents,  of  course,  the 
passage  of  hght  through  the  pupil :  it  is  called  cata- 
ract. This  opaque  lens  we  then  remove  from  the  ej^e, 
and  replace  it  by  a  strong  convex  lens  in  the  specta- 
cles. Whilst  the  lens  has  been  turning  yellow,  all  the 
person's  light  has  been  yellow  ;  so  that,  when  the  lens 
is  removed,  the  impression  will  be  that  of  the  comple- 
mentary color, — bluish.  Many  old  persons  whom  I 
have  operated  on  for  cataract,  after  it  was  removed, 
and  they  were  able  to  use  their  sight,  complained  that 
every  thing  was  blue ;  that,  for  instance,  their  chil- 
dren's faces  appeared  blue :  and  they  naturally  often 
expressed  considerable  disappointment  that  life  was  to 
be  to  them  wholly  bluish.  This  is  not  true  color-blind- 
ness, and  soon  wears  off.  Santonine,  or  worm-seed, 
causes,  when  taken,  all  objects  to  appear  a  bright  yel- 
low,  or   sometimes   its   complementary   color,    violet. 


INTEODUCTION.  XVU 

The  effect  is  not  permanent,  and  passes  off  in  a  few 
hours. 

Another  physiological  fact  in  relation  to  color-per- 
ception is  veiy  important,  and  seems  to  be  generally 
quite  unknown  or  neglected.  Ai'ound  the  point  of  best 
vision  in  the  centre  of  the  retina  is  a  zone  where  we 
perceive  all  of  the  three  so-called  base  colors, — red, 
gi'een,  and  violet.  Outside  of  this  there  is  another 
zone,  in  which  we  have  a  perception  of  only  two; 
namel}',  green  and  violet ;  and  again,  bej'ond  this,  on 
the  retina,  only  blue  or  violet  is  perceived.  We  shall 
hereafter  see  how  these  zones  resemble  color-blindness. 


/ 


EXPLANATION  OF  THE  COLORED  PLATE. 


Kepeated  and  inexcusable  mistakes  have  been  made  in 
Europe  in  reference  to  this  colored  plate  of  Prof.  Holmgren. 
It  has  been  spoken  of  as  if  intended  to  be  used  to  test  for 
color-blindness,  and  has  also  been  so  used.  But,  as  he  ex- 
pressly states,  it  is  only  intended  to  illustrate  the  characteristic 
mistakes  of  the  color-bUnd,  and  the  colors  of  the  sample 
worsteds  to  be  employed. 

I.    The  Gkeen  Test. 

If  the  person  examined  takes  any  of  the  confusion-colors  (1 
to  5)  to  put  with  the  green,  he  proves  himself  color-blind ;  or 
even  if  he  seems  to  want  to  put  them  together. 

n.  a.    The  Pubple  Test.    {This  contains  Bed  and  Violet.) 

The  color-blind  puts  with  it  the  colors  6  to  7,  always  a 
deeper  color. 

If  he  puts  only  purple  colors,  he  is  incojnpletely  color-blind. 

If  he  takes  blue  or  violet,  like  6  and  7,  or  both,  either  with 
or  without  purple,  he  is  completely  red-blind. 

If  he  takes  green  or  gray,  like  8  and  9,  or  one  alone,  with  or 
without  purple,  he  is  completely  green-blind. 

n.  b.    The  Eed  Test.    [Not  necessary  to  he  vsed.) 

Here  the  red-blind  puts,  with  the  red,  dark  green  and  brown 
(10  and  11),  which  are  much  darker  than  the  test. 

The  green-blind  puts,  with  the  red,  lighter  green  and  brown 
than  the  test. 

The  violet-blind  matches,  with  the  purple,  red,  orange,  and 
purple. 

xiz 


COLOR-BLINDNESS: 

ITS  DANGERS  AND  ITS  DETECTION. 


CHAPTER  I. 

HISTORICAL  CASES   OF  COLOR-BLESTDNESS. 

There  seems  no  good  reason  to  doubt  that 
color-blindness  has  existed  at  all  times  in  man. 
It  is  therefore  certainly  very  curious  that  its  de- 
tection, and  consequent  mention  in  literature,  is 
so  very  recent.  A  case  of  Dr.  Tuberville's  (1684) 
has  been  quoted  and  referred  to  as  one  of  color- 
blindness. In  a  letter  to  the  Royal  Society,  Lon- 
don, Aug.  4,  1684,  he  says,  "A  maid  two  and 
twenty  years  old  came  to  me  from  Banbury,  who 
could  see  very  well,  but  no  color  beside  black  and 
white.  She  had  such  scintillations  by  night  (with 
the  appearances  of  bulls,  bears,  &c.)  as  terrified 
her  very  much.  She  could  see  to  read  sometimes 
in  the  greatest  darkness  for  almost  a  quarter  of  an 
hour." 

This  is  too  indefinite  to  be  admitted  as  a  case 
of  color-blindness  recognized  at  that  date.  We 
probably  shall  hunt  literature  in  vain  for  mention 
of  color-blindness  till  nearly  a  hundred  years  later, 


22  COLOR-BLINDNESS  : 

when  we  come  (in  1777)  to  Mr.  Huddart's  account 
of  the  shoemaker  Harris  of  Maryport,  in  Cumber- 
land, Eng.  This  case  is  historic,  and  the  descrip- 
tion perfect  in  its  way,  rendering  it  quite  worthy 
of  being  given  here  in  full.  Huddart  writes  to 
Rev.  J.  Priestley, — 

"  I  have  known  Harris  ten  years,  and  had  frequent  oppor- 
tunities of  conversing  with  him.  I  had  often  heard  from 
others  that  he  could  discern  the  form  and  magnitude  of  all 
objects  very  distinctly,  but  could  not  distinguish  colors. 
This  report  having  excited  my  curiosity,  I  conversed  with 
him  frequently  on  the  subject.  The  account  he  gave  was 
this  :  that  he  had  reason  to  believe  other  persons  saw  some- 
thing in  objects  which  he  could  not  see ;  that  their  language 
seemed  to  mark  qualities  with  confidence  and  precision 
which  he  could  only  guess  at  with  hesitation,  and  frequently 
with  error.  His  first  suspicion  of  this  arose  when  he  was 
about  four  years  old.  Having  by  accident  found  in  the 
street  a  child's  stocking,  he  carried  it  to  a  neighboring  house 
to  inquire  for  the  owner.  He  observed  the  people  called  it  a 
red  stocking,  though  he  did  not  understand  why  they  gave 
it  that  denomination,  as  he  himself  thought  it  completely 
described  by  being  called  a  stocking.  The  circumstance, 
however,  remained  in  his  memory,  and,  together  with  sub- 
sequent observations,  led  him  to  the  knowledge  of  his  de- 
fect. As  the  idea  of  color  is  among  the  first  that  enters  the 
mind,  it  may  perhaps  seem  extraordinary  that  he  did  not 
observe  his  want  of  it  still  earlier.  This,  however,  may  in 
some  measure  be  accounted  for  from  the  circiunstance  of 
his  family  being  Quakers,  among  whom  a  geneial  uniform- 
ity of  colors  is  known  to  prevail.  He  observed,  also,  that, 
when  young,  other  children  could  discern  cherries  on  a  tree 
by  some  pretended  difference  of  color,  though  he  could  only 
distinguish  them  from  the  leaves  by  their  difference  of  size 
and  shape.  He  observed,  also,  that,  by  means  of  this  dif- 
ference of  color,  they  could  see  the  cherries  at  a  greater  dis- 
tance than  he  could,  though  he  could  see  other  objects  at  as 
great  distance  as  they;  that  is,  where  the  sight  was  not 
assisted  by  the  color.     Large  objects  he  could  see  as  well  aa 


ITS   DANGEES  AND  ITS   DETECTION.  3 

other  persons ;  and  even  the  smaller  ones,  if  they  were  not 
enveloped  in  other  things,  as  in  the  case  of  cherries  among 
the  leaves.  I  believe  he  could  never  do  more  than  guess 
the  name  of  any  color ;  yet  he  could  distinguish  white  from 
black,  or  black  from  any  light  or  bright  color.  Dove  or 
straw  color  he  called  white,  and  different  colors  he  frequent- 
ly called  by  the  same  name ;  yet  he  could  discern  a  differ- 
ence between  them  when  placed  together.  In  general,  colors 
of  an  equal  degree  of  brightness,  however  they  might  other- 
wise differ,  he  frequently  confounded  together ;  yet  a  striped 
ribbon  he  could  distinguish  from  a  plain  one,  but  he  could 
not  tell  what  the  colors  were  with  any  tolerable  exactness. 
Dark  colors  in  general  he  often  mistook  for  black,  but  never 
imagined  white  to  be  a  dark  color,  nor  dark  to  be  a  white 
color.  He  was  an  intelligent  man,  and  very  desirous  of 
understanding  the  nature  of  light  and  colors,  for  which  end 
he  had  attended  a  course  of  lectures  in  natural  philosophy. 
He  had  two  brothers  in  the  same  circumstances  as  to  sight, 
and  two  other  brothers  and  sisters,  who,  as  well  as  their 
parents,  had  nothing  of  this  defect.  One  brother  is  master 
of  a  trading-vessel.  I  met  him,  and  asked  him  whether  he 
had  ever  seen  a  rainbow.  He  replied  he  had  often,  and 
could  distinguish  the  different  colors ;  meaning  only  that  it 
was  composed  of  different  colors,  for  he  could  not  tell  what 
they  were.  A  piece  of  ribbon  he  without  difficulty  pro- 
nounced striped,  and  not  plain.  The  several  stripes  of  white 
he  uniformly  so  called.  The  four  black  stripes  he  was  de- 
ceived in ;  for  three  of  them  he  thought  brown,  though  they 
were  exactly  of  the  same  shade  with  the  other,  which  he 
properly  called  black.  The  light  green  he  called  yellow, 
but  he  was  not  very  positive.  He  said,  '  I  think  that  is 
what  you  call  yellow.'  The  middle  stripe,  which  had  a 
slight  tinge  of  red,  he  called  a  sort  of  blue.  But  he  was 
most  of  all  deceived  by  the  orange  color :  of  this  he  spoke 
very  confidently,  saying,  '  This  is  the  color  of  grass  :  this  is 
green.'  I  also  showed  him  a  great  variety  of  ribbons,  the 
color  of  which  he  sometimes  named  rightly,  and  sometimes 
as  differently  as  possible  from  the  true  colors.  These  ex- 
periments were  made  in  the  daytime,  and  in  a  good  light. 
I  asked  him  whether  he  imagined  it  possible  for  all  the 
various  colors  he  saw  to  be  mere  difference  of   light  and 


4  COLOE-BLINDNESS  : 

shade ;  whether  he  thought  they  could  be  various  degrees 
between  white  and  black,  and  that  all  colors  could  be  com- 
posed of  these  two  mixtures  only.  With  some  hesitation  he 
replied,  No :  he  did  imagine  there  was  some  other  differ- 
ence." 

In  1779  Mr.  J.  Scott  reported  his  own  case  in  a 
letter  to  Rev.  Mr.  Whisson,  Trinity  College,  and 
communicated  by  the  Rev.  Michael  Lort.  He 
says  that  a  full  red  and  full  green,  pale  blue  and 
pink,  deep  red  and  blue  gave  him  the  same  sensa- 
tion ;  but  he  readily  distinguished  yellow  and 
deep  blue.  Tlie  claret  color  of  a  garment  seemed 
to  him  deep  black. 

We  must  again  seek  in  vain  in  literature  for 
cases  of  color-blindness  till  we  come,  in  1794,  to  the 
English  chemist  Dalton's  description  of  his  own  vis- 
ion. His  report  excited  so  much  attention,  that 
liis  name  became  attached  to  this  chromatic  defect, 
which,  by  general  consent,  is  now  among  nearly 
all  nations  called  color-blindness,  not  only  from  a 
desire  not  to  connect  so  distinguished  a  man's 
name  as  Dalton  with  a  physical  defect,  but  as  also 
being  nearer  the  truth,  since  only  the  red-blind 
are  Daltonians.  Dalton's  case  is  as  interesting 
as  historical.     He  says,  — 

"It  has  been  observed  that  our  ideas  of  colors,  sounds, 
tastes,  &c.,  excited  by  the  same  object,  may  be  very  differ- 
ent in  themselves  without  our  being  aware  of  it,  and  that  we 
may  nevertheless  converse  intelligibly  concerning  such  ob- 
jects as  if  we  were  certain  the  impressions  made  by  them  on 
our  minds  were  exactly  similar.  It  will,  however,  scarcely 
be  supposed  that  any  two  objects,  which  are  every  day  before 
us,  should  appear  hardly  distinguishable  to  one  person,  and 
very  different  to  another,  without  the  circumstance  immedi- 
ately suggesting  a  difference  in  their  faculties  of  vision ;  yet 
Buch  is  the  fact,  not  only  with  regard  to  myself,  but  to  many 


ITS   DANGERS   AND   ITS   DETECTION.  5 

others  also.  Xotwithstanding  the  occasional  study  of 
botany,  I  was  never  convinced  of  a  peculiarity  in  my  vision 
till  I  accidentally  observed  the  color  of  the  flower  Geranium 
zonale  by  candle-light  in  1792.  The  flower  was  pink,  but 
it  appeared  to  me  almost  an  exact  sky-blue  by  day.  In  can- 
dle-light, however,  it  was  astonishingly  changed,  not  halving 
then  any  blue  in  it,  but  being  what  I  called  red,  —  a  color 
which  forms  a  striking  contrast  to  blue.  Friends,  when 
asked,  all  agreed  that  the  color  was  not  materially  different 
from  what  it  was  by  daylight,  except  my  brother,  who  saw 
it  in  the  same  light  as  myself.  Two  years  afterwards  I 
commenced  an  investigation  of  the  subject,  assisted  by  a 
friend.  My  observation  began  with  the  solar  spectrum,  or 
colored  image  of  the  sun,  exhibited  in  a  dark  room  by  means 
of  a  glass  prism.  I  found  that  persons  in  general  distinguish 
six  kinds  of  color  in  the  solar  image ;  namely,  red,  orange, 
yellow,  green,  blue,  purple.  To  me  it  is  quite  otherwise  :  I 
see  only  two,  or  at  most  three,  distinctions.  These  I  should 
call  yellow  and  blue,  or  yelloio,  blue,  and  purple.  My  yellow 
comprehends  the  red,  orange,  yellow,  and  green  of  others ;  and 
my  blue  and  purple  coincide  with  theirs.  That  part  of  the 
image  which  others  call  red  appears  to  me  little  more  than 
a  shade,  or  defect  of  light ;  after  that,  the  orange,  yellow, 
and  green  seem  one  color,  which  descends  pretty  uniformly 
from  an  intense  to  a  rare  yellow,  making  what  I  should  call 
different  shades  of  yellow.  The  difference  between  the 
green  part  and  the  blue  part  is  very  striking  to  my  eye  :  they 
seem  to  be  strongly  contrasted.  That  between  the  blue  and 
purple  is  much  less  so.  The  purple  appears  to  be  blue  much 
darkened  and  condensed." 

The  next  cases  reported  in  order  of  time  are  by 
Dr.  Nicholl,  1816  and  1818.  One  was  a  boy 
eleven  years  old,  who  was  color-blind,  like  Dalton. 
The  other  was  a  man  aged  forty-nine,  who  reported 
thus :  — 

"  The  color  I  am  most  at  a  loss  with  is  green ;  and,  in 
attempting  to  distinguish  it  from  red,  it  is  nearly  guess- 
work. Scarlet  in  most  cases  I  can  distinguish,  but  a  dark 
bottle-green  I  could  not,  with  any  certainty,  from  brown. 


6  COLOR-BLINDNESS  : 

Light  yellow  I  know ;  dark  yellow  I  might  confound  with 
light  brown,  though  in  most  cases,  I  think,  T  should  know 
them  from  red.  The  different  shades  of  red  and  green,  I 
know  not  to  which  they  belong  ;  but,  when  they  are  before 
me,  I  see  a  difference  in  the  shade.  Though  I  see  different 
shades  in  looking  at  a  rainbow,  I  should  say  it  was  a  mix- 
ture of  yellow  and  blue,  —  yellow  in  the  centre,  and  blue 
towards  the  edges." 

These  cases  are  about  all  which  may  be  properly 
considered  historic.  I  have  referred  to  the  origi- 
nal accounts,  and  quoted  from  them.  It  may  be 
noticed  that  mention  of  what  the  several  persons 
called  colors  —  i.e.,  the  names  they  gave  them  on 
presentation — has  been  generally  omitted.  The 
reason  of  this  will  be  seen  later.  It  need  only 
here  be  remarked,  that  asking  the  examined,  to 
name  colors  is  in  reality  no  test  of  their  color- 
perception  ;  and,  where  this  alone  has  been  done, 
their  color-blindness  cannot  be  accepted  as  proved. 


ITS   DAis-GEES   AXD  ITS   DETECTIOK. 


CHAPTER  II. 


COLOE-BLIXD   MISTAKES. 


It  will  be  interesting  to  note  what  mistakes 
their  chromatic  deficiency  causes  the  color-blind 
to  make,  and  therefore  well  worth  our  while  to 
listen  to  their  own  report,  as  well  as  that  of  their 
examiners.  Xot  only  shall  we  find  it  curious  and 
interesting,  but  from  a  long  series  of  cases  we  may 
able  to  deduce,  as  has  been  done,  some  general 
laws  and  classification  of  tliis  peculiar  visual  condi- 
tion. Commencing  with  the  cases  I  have  referred 
to  as  historical :  Dalton  said  the  color  of  a  florid 
complexion  seemed  dull,  opaque,  blackish  blue 
upon  a  white  ground.  Diluted  black  ink  on  white 
paper  gives  a  color  much  resembling  a  florid  com- 
plexion. It  has  no  resemblance  to  the  color  of 
blood.  Blood  appeared  not  unlike  that  color  called 
bottle-green.  Grass  appeared  a  very  little  differ- 
ent from  red.  The  face  of  a  laurel-leaf  is  a  good 
match  to  a  stick  of  red  sealing-wax,  and  the  back 
of  the  leaf  answers  to  the  lighter  red  of  wafers. 
Green  woollen  cloth  —  such  as  is  used  to  cover 
tables  —  appeared  a  dull  brownish-red  color.  A 
mixture  of  two  parts  mud  and  one  red  would  come 


8  COLOE-BLINDNESS  : 

near  it.  It  resembled  a  red  soil  just  turned  up  by 
the  plough.  "When  this  kind  of  cloth  loses  its 
color,  as  other  people  say,  and  turns  yellow,  then 
it  appears  to  me  a  pleasant  green.  Very  light- 
green  paper,  silk,  &c.,  is  white  to  me."  Blue  was 
the  same  to  him  as  to  other  people,  both  by  day- 
light and  candle-light.  "Colors  appear  to  me 
much  the  same  by  moonlight  as  they  do  by  can- 
dle-light. By  lightning  and  the  electric  light  they 
appear  as  by  daylight.  A  light-drab  woollen  cloth 
seems  to  resemble  a  light  green  by  day.  My  idea 
of  brown  I  obtain  from  a  piece  of  white  paper 
heated  almost  to  ignition.  This  color  by  daylight 
seems  to  have  a  great  affinity  to  green.  Browns 
seem  to  me  very  diversified  :  some  I  should  call  red. 
Dark-brown  woollen  cloth  I  should  call  black." 

A  most  amusing  account  was  given  by  Babbage 
of  the  incidents  attending  the  presentation  of  Dal- 
ton  at  court :  — 

"  Firstly  he  was  a  Quaker,  and  would  not  wear  the 
sword,  which  is  an  indispensable  appendage  of  ordinary 
court-dress.  Secondly,  the  robe  of  a  doctor  of  civil  laws 
was  known  to  be  objectionable  on  account  of  its  color, — 
scarlet,  —  one  forbidden  to  Quakers,  Luckily  it  was  recol- 
lected that  Dalton  was  afflicted  with  the  peculiar  color- 
blindness which  bears  his  name,  and  that,  as  the  cherries 
and  the  leaves  of  a  cherry-tree  were  to  him  of  the  same 
color,  the  scarlet  gown  would  present  to  him  no  extraordi- 
nary appearance.  So  perfect,  indeed,  was  the  color-blind- 
ness, that  this  most  modest  and  simple  of  men,  after  having 
received  the  doctor's  gown  at  Oxford,  actually  wore  it  for 
several  days  in  happy  unconsciousness  of  the  effect  he  pro- 
duced on  the  street."  —  Scientific  London,  1874,  p.  38. 

Professor  Whewell  reports  having  asked  Dalton 
what    the    bright-scarlet    gown    which    he    wore 


ITS   DANGEES   AND   ITS   DETECTION.  9 

resembled,  and  he  pointed  to  some  of  the  ever- 
greens outside  of  the  window,  and  said,  that  to  his 
eje  their  colors  were  quite  alike.  On  the  other 
hand,  the  lining  of  the  gown,  which  was  pink  silk, 
he  could  not  distinguish  from  sky-blue. 

The  first  case  recorded  —  Harris  the  shoemaker 
—  noticed,  when  an  infant,  what  the  color-blind 
nearly  always  do,  namely,  the  inability  to  distin- 
guish any  red  fruits  from  the  surrounding  green 
leaves.  Recognition  of  their  chromatic  defect 
dates  not  infrequently  from  companions  being  able 
to  pick  strawberries,  cherries,  (Sec,  more  quickly. 
One  of  Dr.  Colquhoun's  patients  says,  — 

"I  cannot  perceive  a  bit  of  red  sealing-wax  if  thrown 
down  upon  the  grass,  nor  a  piece  of  scarlet  cloth  hung  upon 
a  hedge,  which,  I  was  told,  was  to  be  seen  a  mile  off.  I 
once  gathered  some  lichen,  as  a  great  curiosity,  from  the  roof 
of  a  friend's  fishing-house.  I  thought  it  was  of  a  bright 
scarlet,  from  its  seeming  to  be  of  the  same  color  as  the  tiles  : 
in  reality  it  was  a  bright  green.  On  another  occasion  I  per- 
ceived no  difference  in  the  complexion  of  a  foreign  lady, 
who  had  purposely  substituted  Prussian  blue  for  her  rouge." 

Dr.  Nicholl  says  of  a  boy,  eleven  years  old,  — 

"  I  placed  a  scarlet  paper  on  the  grass,  and  afterwards  a 
green  baize.  He  said  that  the  grass  and  the  baize  were  of  the 
same  color  as  the  paper,  but  that  they  were  a  shade  lighter. 
I  made  him  put  on  a  pair  of  green  spectacles,  which  he 
called  red  glasses.  He  said  that  everybody  and  every  thing 
in  the  room  had  a  reddish  cast  when  seen  through  them. 
The  border  of  the  room  had  a  blue  leaf  with  a  green  edge : 
this  he  called  a  blue  leaf  with  a  red  border.  A  woman 
passed  by  with  a  basket  on  her  arm.  He  told  his  mother  that 
the  woman  had  fowls  in  it,  for  that  he  saw  the  red  feathers 
hanging  out :  these  proved  to  be  green  leaves  with  which  she 
had  covered  her  butter.  He  told  me,  '  What  you  call  i^urple 
and  pink  and  blue  are  so  like  each  other,  that  1  cannot  well 
know  one  from  the  other.'     He  also  called  the  gray  eyes  of 


10  COLOR-BLINDNESS  : 

his  sister  a  bluish  red.  A  blood-relative  of  this  lad  was  in 
the  navy,  and  purchased  a  blue  uniform  coat  and  waistcoat, 
with  red  breeches  to  match  the  blue.  I  showed  him  a  doi- 
ly which  was  red,  having  a  leaf  of  the  same  color  traced 
out  on  it,  and  I  asked  him  the  color  of  it.  He,  having  been 
so  often  mistaken  and  laughed  at,  said,  with  an  air  of  tri- 
umph, '  Why  the  groundwork  is  red ;  but  the  leaf  is  of  course 
green.' " 

Dr.  Nichoirs  second  case,  a  gentleman  forty-nine 
years  old,  said,  — 

"  If  railings  were  painted  red,  I  could  not  distinguish 
them  from  the  grass.  The  grass  in  full  verdure  appears  to 
me  what  other  people  call  red ;  and  the  fruit  on  trees,  when 
red,  I  cannot  distinguish  from  the  leaves,  unless  when  I 
am  near  it.  A  cucumber  and  a  boiled  lobster  I  should  call 
the  same  color,  making  allowance  for  the  variety  of  shade  to 
be  found  in  both ;  and  a  leek  in  luxuriance  of  growth  is  to 
me  more  like  a  stick  of  sealing-wax  than  any  thing  I  can 
compare  it  with.'  " 

In  further  illustration  of  the  sort  of  mistakes 
the  color-blind  make,  I  here  quote  some  of  Pro- 
fessor Wilson's  cases.  A  middle-aged  gentleman 
says,  — 

"  As  far  as  I  can  tell,  the  following  expresses  my  experi- 
ence as  to  colors.  Yellow  is  the  brightest  color ;  blue,  nearly 
as  bright.  These  two  are  the  only  ones  I  see  distinctly  in 
the  rainbow.  Red  I  can  distinguish  when  bright ;  but  deli- 
cate shades  I  confound  with  stone-color  or  gray.  Green  I 
have  no  distinct  conception  of.  According  to  its  different 
shades,  it  appears  black,  brown,  red,  yellow,  blue,  and  gray. 
I  cannot  distinguish  at  any  distance  the  ri^^e  cherries  on  a 
tree,  or  strawberries  from  their  leaves.  I  have  no  concep- 
tion of  what  is  meant  by  complementary  colors,  or  of  the 
agreement  of  different  colors  when  blended  together ;  as,  for 
instance,  what  kind  of  a  carpet  accords  with  red  curtains  in 
a  room.  AVith  regard  to  my  want  of  perception  of  green,  it 
appears  to  me  that  the  blue  and  the  yellow  rays  neutralize 
each  other,  and,  when  in  equal  proportions,  constitute  what  is 


ITS   DANGERS   AND   ITS   DETECTION.  11 

really  no  color,  varying  all  the  way  from  a  very  light  drab 
or  gray  to  a  clingy  black.  When  the  blue  rays  predominate, 
it  appears  a  blue  drab;  and,  when  the  yellow  rays  are  in  ex- 
cess, it  appears  a  yellow  drab.  When  the  blue  and  yellow 
are  properly  blended,  a  lady's  green  silk  dress  appears  to  me 
very  similar,  and  no  more  glaring  than  a  drab  silk.  The 
dry  dirt  of  the  street  I  could  equally  suppose  to  be  green 
I  also  confound  red  and  brown  frequently.  I  could  not  dis- 
tinguish between  treacle  and  blood  si^ilt  in  a  road  by  day- 
light." 

Another  gentleman  gives  a  very  interesting  illus- 
tration of  the  extent  of  his  color-blindness  in  ref- 
erence to  red  and  green.  When  acting  as  assistant 
to  the  engineer  of  the  Granton  Kailway,  he  fre- 
quently returned  in  the  evening  from  Granton  to 
Edinburgh  on  one  of  the  engines,  without,  how- 
ever, taking  any  part  in  managing  it.  On  these 
occasions  he  observed,  that,  although  his  undivided 
attention  was  directed  towards  the  signal  lamps, 
the  light  of  which  was  visible  to  him  a  long  way 
off,  he  could  not,  till  he  was  close  upon  them,  dis- 
tinguish whether  they  were  red  or  green.  He  feels 
certain  that  he  could  tell  a  blue  light  from  a  red 
light  at  a  distance  which  would  make  green  and 
red  appear  the  same. 

Another  gentleman  was,  like  many  other  color- 
blind persons,  a  great  lover  of  fine  arts,  and  a 
skilful  draughtsman.  He  was  led  in  consequence, 
early  in  life,  to  discover  his  inability  to  arrange 
his  own  palette,  and  was  accustomed  to  rely  upon 
a  relative  to  select  his  colors,  whilst  he  had  no 
difficulty  in  graduating  their  shades.  In  the  rain- 
bow he  distinguishes  blue,  yellow,  and  orange. 
Green  he  never  sees  in  it,  and  he  is  very  uncertain 
as  to  red.     In  colored  objects  he  has  no  difficulty 


12  COLOR-BLINDNESS  : 

with  blue  or  j^ellow ;  but  he  stumbles  at  red  and 
green,  and  olive  and  brown.  Green  moss  and  red 
and  green  velvet  make  the  same  impression  on  his 
eye,  so  far  as  color  is  concerned.  He  is  foiled  also 
by  worsteds  of  these  colors,  and  on  one  occasion 
betrayed  his  peculiarity  of  vision  by  his  inability 
to  see  the  contrast  between  the  scarlet  berries  and 
green  leaves  of  the  mountain-ash.  On  another 
occasion  he  was  surprised  to  find^  on  returning 
home  from  a  journey,  that  a  letter  which  he  had 
written  home  during  his  absence  was  one-half  in 
black  and  the  other  in  red  ink.  A  red-brick 
house,  which  to  others  is  a  conspicuous  object  in 
the  landscape,  even  at  a  great  distance,  is  to  him 
an  inconspicuous  one,  and  made  out  with  great 
difficulty  solely  by  its  form. 

"  Green  and  red  I  cannot  distinguish  from  each  other. 
Red  cabbage  growing,  pickled,  or  in  infusion,  are  all  the 
most  beautiful  blue  I  can  conceive;  and  it  was  by  not  ob- 
serving any  change  by  acids  in  the  infusion  of  red  cabbage, 
when  attending  Professor  Hope's  chemistry-class,  where  I 
used  to  stare  for  the  whole  hour  expecting  to  see  the  change, 
that  I  first  became  fully  convinced  of  my  great  defect. 
Red,  again,  in  the  lips,  cheeks,  nose  (red),  gooseberries,  in- 
flammations, and  the  like,  looks  blue  to  me !  (I  never  saw 
a  red  nose  in  my  life ;  )  and  yet,  in  recently  taking  up  an  oil- 
paint,  to  illustrate  to  another  my  conception  of  the  color  of 
the  lips,  you  will  be  astonished  to  hear  that  I  took  up  a 
green  (terre  verte).  On  another  occasion  I  was  very  much 
annoyed  at  a  little  boy  who  could  tell  a  blue  line  of  w^ater- 
color,  drawn  across  my  finger,  from  blood :  I  could  see  no 
difference.  Strawberries,  cherries,  &c.,  I  can  recognize  with- 
out the  slightest  difficulty ;  but  I  don't  trouble  myself  about 
their  color :  I  see  only  a  difference  as  regards  what  I  call 
shade.  Pinks,  lilacs,  purples,  and  blues  are  all  the  same 
color,  only  differing  in  intensity.  Browns,  russets,  maroons, 
olives,  citrines,  and  a  host  of  others,  are  just  any  thing  I 


ITS   DANGERS   AND   ITS    DETECTION.  13 

can  guess  at;  but  I  never  get  farther  than  red,  brown,  or 
green.  The  names  of  the  other  colors  I  don't  think  I  ever 
uttered.  Indeed,  I  never  speak  of  colors,  unless  I  cannot 
avoid  it;  and  the  only  practical  mistake  I  ever  made  in  re- 
gard to  them  was  purchasing  a  purple  neckcloth  under  the 
impression  it  was  black.  That  was  the  only  mistake,  for  a 
good  reason :  I  never  bought  a  colored  piece  of  dress  alone, 
either  before  or  since.  A  piece  of  railway  red  signal-glass, 
and  another  of  green  signal-glass,  held  up  together,  close  to 
the  eye  in  daylight,  appeared  to  be  shades  of  the  same 
color." 

An  engraver  reports,  — 

"  Strange  as  it  may  appear,  my  defective  vision  is,  to  a 
certain  extent,  a  useful  and  valuable  quality.  Thus  :  an  en- 
graver has  two  negative  colors  to  deal  with ;  i.e.,  white  and 
black.  Xow,  when  I  look  at  a  picture,  I  see  it  only  in  white 
and  black,  or  light  and  shade ;  and  any  want  of  harmony 
in  the  coloring  of  a  picture  is  immediately  made  manifest 
by  a  corresponding  discord  in  the  arrangement  of  its  light 
and  shade,  or,  as  artists  term  it,  the  effect.  I  find  at  times 
many  of  my  brother-engravers  in  doubt  how  to  translate 
certain  colors  of  pictures,  which  to  me  are  matters  of  de- 
cided certainty  and  ease.  Thus  to  me  it  is  valuable.  From 
childhood  I  have  been  totally  unable  to  retain  certain  colors 
in  my  mind,  nor  able  to  give  their  names  when  shown  to 
me  a  second  time.  This  defect  applies  more  particularly  to 
compound  colors,  such  as  green,  purple,  orange,  and  brown 
(this  color  I  can  never  define)  ;  also  the  difference  between 
pink  and  pale  blue,  reds  and  yellows,  blues  and  greens,  reds 
and  greens ;  but  the  appreciation  of  the  various  shades  of 
colors  (or  the  weight  of  colors,  as  I  may  term  it)  is  exceed- 
ingly nice  and  critical.  A  few  years  ago  I  went  to  a  dra- 
per's to  buy  some  green  baize,  but  unfortunately  bought  a 
very  bright  red,  which  was  excessively  painful  to  my  eyes 
by  lamplight,  but  agreeable  enough  by  daylight." 

An  amateur  artist,  who  also  worked  with  cray- 
ons, found  his  defect  an  advantage,  and  reports,  — 

"I  have  myself  a  distinct  perception  of  the  whole  spec- 
trum, with  the  exception  of  the  red  and  green,  which  seem 


14  COLOR-BLINDNESS : 

to  be  a  very  near  repetition  of  the  same  colors ;  the  differ- 
ence between  them  being  to  my  eye  much  more  marked  by 
some  accidental  variation  of  tone  rather  than  of  tint,  which 
to  others  is  frequently  imperceptible.  The  flowers  of  a 
fuchsia,  the  berries  of  mountain-ash  and  holly,  are  scarcely 
distinguishable  to  me,  excepting  by  their  tone  or  form." 

He  also  adds,  "  I  recollect  the  late  Lord  V.  joking  his 
wife  for  wearing  a  scarlet  dress.  She  assured  him  it  was 
bright  green ;  and,  comparing  notes  with  him,  I  found  that 
our  defect  of  vision  was  precisely  the  same,  although  he 
had  been  scarcely  aware  of  it  till  that  time.  My  brother, 
who  has  the  same  trouble,  once  picked  up  a  red-hot  coal, 
asking  what  that  funny  green  thing  was." 

Another  case  writes  as  follows :  — 

"I  do  not  think  I  should  easily  mistake  a  green  for  a 
red,  or  red  for  a  green  ;  but,  if  the  distant  perception  of 
scarlet  (or  red  of  that  nature)  is  a  necessary  qualification 
for  an  engine-driver  in  the  conduct  of  a  train,  I  shall  be 
careful,  '  come  what  come  may,'  never  to  offer  myself  in 
tliat  capacity  to  a  railway  company.  At  a  distance  of  about 
sixty  yards  it  would  puzzle  me  to  distinguish  the  color  of  a 
soldier's  coat,  although  the  general  outline  of  the  figure 
would  enable  me  to  pronounce  upon  its  being  that  of  a 
soldier." 

^    An  admiral  in  the  British  service  writes,  — 

"  A  younger  brother  of  mine,  long  since  dead,  was  fond 
of  drawing ;  yet  once  he  painted  a  red  tree  in  a  landscape 
without  being  aware  he  had  done  so.  I  myself,  though  fond 
of  drawing,  never  attempted  to  color,  as  I  should  have  done 
the  same,  unless  the  cake  of  color  had  been  properly  marked. 
I  find  that  it  is  not  that  I  do  not  see  a  distinction  between 
two  colors  when  placed  near  each  other,  as  in  patterns  or 
bales  of  cloth;  but  I  should  hardly  distinguish  a  red  jacket 
hung  on  a  tree,  unless  quite  fresh  from  the  loom.  A  red- 
tiled  barn  I  should  not  distinguish  in  a  landscape,  but  from 
knowing  tiles  are  red.  The  shades  of  green,  of  brown,  and 
of  red,  perplex  me  most.  Bright  scarlet  is  unmistakable  to 
me  ;  but  I  chose  a  pair  of  green  trousers  once,  thinking 
they  were  brown.     As  for  signal-lanterns,  I  should  know 


ITS   DANGERS   AND   ITS   DETECTION.  15 

the  difference  between  red  and  green  if  they  were  shown 
together;  but  I  should  be  sorry  if  the  safety  of  a  train 
depended  on  my  lookout,  when  one  light  alone  was  exhibited 
as  danger  or  no  danger." 

A  young  physician  answers,  "  Having  often  observed  a 
railway  signal-light,  seen  from  my  window,  I  am  convinced 
that  its  colors  would  be  lost  upon  me ;  nor  dare  I  trust  to 
their  flags.  I  never  venture  on  the  purchase  of  colored 
articles  without  a  companion  to  appeal  to." 

Professor  IN",  says,  "I  suppose  I  can  sometimes  distin- 
guish red  in  some  objects,  but  probably  this  is  from  knowing 
that  they  are  usually  of  this  color.  At  any  rate,  I  am  quite 
sure  that  I  should  make  a  dangerous  railway-signal  man,  as 
I  most  certainly  would  not  know  a  red  flag  from  a  green 
one." 

An  architect  reports  having  to  release  a  pupil- 
apprentice  in  consequence  of  finding  him  copy  a 
brown  house  in  bluish-green  paint,  the  sky  rose- 
color,  and  roses  blue. 

A  tradesman  reports  his  boy  offering  pink  and 
pale-green  jDaper  as  good  matches,  and  getting  his 
master  into  frequent  trouble  by  binding  books  in 
wrong  colors. 

A  manufacturer  reports  that  one  of  his  weavers 
had  to  have  the  red  and  green  threads  selected  by 
another,  as  he  could  not  distinguish  them. 

A  carver  and  gilder,  who  was  color-blind,  had  a 
son  who  painted  a  head  with  the  face  muddy 
green,  which  he  conceived  to  be  vermilion.  A 
brother  of  this  person,  an  artist  by  profession, 
knew  no  difference  by  gaslight  between  the  vari- 
ously-colored bottles  in  a  druggist's  window,  and 
could  not  distinguish  the  red  from  the  green  signal- 
lamp  at  a  railway-station. 

Six  males  —  uncles,  nephews,  and  cousins  —  in 
one  family  all  belong  to  the  Society  of  Friends; 


16  COLOR-BLINDNESS  : 

and  their  mistakes  in  selecting  articles  of  dress 
have  been  rendered  especially  conspicuous  by  the 
preference  which  members  of  that  religious  body 
give  to  the  least  brilliant  and  most  unconspicuous 
colors.  One  of  their  number  provided  himself 
with  a  bottle-green  coat,  intending  to  purchase  a 
brown  one ;  and  selected  for  his  wife,  who  desired 
a  dark  gown,  a  scarlet  merino.  Another,  who  is 
an  upholsterer,  purchased  scarlet  for  drab,  and 
had  to  rely  upon  his  wife  and  daughters  to  select 
for  him  the  fabrics  needed  in  the  course  of  his  pro- 
fession. A  third,  who  is  a  farmer,  could  not  tell 
red  apples  from  the  surrounding  green  leaves,  ex- 
cept by  their  shape.  All  of  them  confounded  red 
with  green,  olive  with  brown,  and  pink  with  blue ; 
but  they  are  very  expert  at  matching  shades  of 
the  same  color.  One  of  the  younger  men,  whose 
profession  requires  him  to  deal  much  in  colored 
tissues,  has  found  that  the  "  only  way  of  telling 
the  difference  between  scarlet  and  green,  or  blue 
and  crimson,  is  to  take  them  into  a  room  lighted 
with  gas  or  candles,"  when  the  distinction  which 
was  invisible  by  daylight  becomes  apparent. 
Olives  and  browns,  however,  are  as  undistinguish- 
able  by  one  light  as  by  another.  A  minister,  also 
in  the  Society  of  Friends,  selected  scarlet  cloth  as 
the  material  for  a  new  coat. 

As  to  females  with  color-blindness,  Wilson  says 
of  the  Countess  of  D.,  — 

"  Red,  green,  black,  browii,  and  lilac,  she  does  not  ven- 
ture to  name  confidently,  and  greens  and  drabs  are  the  same 
color.  Mountain-ash  or  holly  berries  are  undistinguishable 
from  their  foliage.  Li  sorting  worsteds  she  can  place  no 
confidence  in  herself  in  choosing,  and  all  the  lightest  shades 
of  color  are  liable  to  be  completely  mixed  up.     '  The  yellow 


ITS   DANGERS   AND   ITS   DETECTION.  17 

tints  now  (October)  seen  on  the  trees  appear  to  me  exactly 
the  same  as  those  of  their  spring  shades  :  indeed  I  cannot 
conceive  the  possibility  of  any  one  seeing  them  to  be  dif- 
ferent.' The  term  'yellow'  here  included  all  the  autumn 
tints  of  the  leaves ;  and  therefore  various  shades  of  orange, 
red,  russet,  and  brown  must  have  seemed  identical  with  the 
yellow  green  and  the  bright  green  of  the  spring  leaves." 

A  lady  reports,  "  I  do  not  know  how  to  express  myself 
well  regarding  the  loss  I  am  at  to  distinguish  colors,  as  I 
hardly  understand  lioio  it  is  myself ;  but  I  will  try  to  do  so  as 
clearly  as  I  can.  There  are  many  colors  the  shades  of  which 
I  confound  :  these  are  blue,  lilac,  pink,  and  purple ;  and,  if 
the  various  shades  of  these  colors  were  put  before  me  and 
mixed  together,  I  should  be  quite  confused,  and  could  not 
tell  to  which  each  belongs,  although  I  see  they  are  different. 
In  the  same  way  I  confound  green,  brown,  and  some  of  the 
shades  of  orange.  In  short,  were  I  to  tell  the  name  of  any 
color  correctly,  it  would  be  merely  guesswork.  I  can  enjoy 
the  beauties  of  nature,  and  the  varied  hues  of  the  trees,  &c. ; 
but  that  there  is  some  defect  in  my  vision  I  am  quite  aware. 
Of  this,  also,  I  am  certain ;  I  can  do  nothing  (or  as  yet  have 
not  been  able)  to  improve  it." 

When  engaged  with  colored  worsted-work,  she 
always  has  the  skeins  marked. 

To  this  long  list  of  foreign  and  American  re- 
ports, I  could,  of  course,  now  add  as  many  more 
from  my  own  experience  with  the  color-blind.  I 
will  forbear  giving  but  a  few,  merely  to  show  that 
they  all  can  be  brought  under  the  same  general 
laws. 

Dr.  Blank  writes  me,  "  Possibly  you  may  have 
recollected  that  I  am  myself  of  the  red-green 
group.  In  1854-55  Wilson  of  Edinburgh  added 
me  to  his  list." 

Another  physician  writes  me,  "  I  read  with  in- 
terest 3^our  color-blind  researches  :  for  I  am  shock- 
ingly so,  often  to  my  great  chagrin  and  the  morti- 


18  COLOR-BLINDNESS  : 

fication  of  my  wife  and  daughter,  and,  where  I  feel 
it  most,  in  surgical  practice,  —  color  of  throats, 
gangrene,  ulcers,  coppery-hued  sores,  &c. ;  so  that 
I  have  to  draw  out  the  statements  of  others  for 
my  guidance." 

A  gentleman  tells  me,  "  Yellow  and  blue  are  my 
only  distinct  colors.  Red  is  the  most  indistinct. 
I  cannot  see  certain  shades  of  red.  I  cannot  dis- 
tinguish scarlet  salvias  a  few  rods  away." 

A  member  of  a  well-known  American  color-blind 
family  sends  me  word,  "Red,  brown,  and  green, 
of  about  the  same  depth  or  strength  of  color,  ap- 
pear about  alike  to  me.  The  red  cherry  and  the 
leaf  of  the  tree  look  substantially  alike." 

A  lady,  whose  father  was  color-blind,  writes  me 
of  two  of  her  children,  boys  (three  girls  being 
free  of  the  defect),  that  "  they  do  not  observe 
when  a  flaming  bush  of  Pyrus  Jajjonica  is  in  flower, 
unless  near  enough  to  discern  the  form  of  the 
flower.  After  having  his  attention  directed  to  it, 
one  of  them  said,  '  Oh,  yes !  I  see  the  flowers  now ; 
but  they  are  not  so  bright  as  the  leaves.'  The 
leaves  in  their  young  state  are  of  a  very  yellow 
green.  Neither  of  the  boys  is  near-sighted.  I  first 
noticed  it  in  my  older  boy  when  he  was  five  years 
old.  We  were  in  a  field,  and  the  girls  were  scream- 
ing with  delight  over  such  columbines  all  around 
them.  The  little  boy  said,  'Where  are  they?  I 
don't  see  any  flowers.'  After  having  one  put  in 
his  hand,  and  observing  the  form,  he,  too,  could 
find  them.  There  are  two  colors  my  boys  are 
t[uite  unable  to  learn  to  distinguish.  These  are 
a  light  green  and  a  yellow  brown.  I  do  not  think 
they  see  any  difference  between  them.     I  enclose 


ITS   DANGERS   AND   ITS   DETECTION.  19 

bits  of  tlie  colors  I  mean.  I  omitted  to  mention 
that  my  boys  always  call  crimson  blue." 

The  green  worsted  I  found  almost  the  same  as 
the  shade  used  in  Holmgren's  test,  and  the  yellow- 
ish brown  just  the  color  the  color-blind  will  select 
among  the  first,  if  not  the  very  first,  to  match  the 
green. 

A  colleague  at  a  distance,  regarded  by  his  wife 
as  very  deficient  in  color-perception,  asked  my 
opinion.  I  sent  him  my  test-worsteds;  and  the 
matches  he  returned  me  were  amusing,  fully  sub- 
stantiating the  lady's  opinion  and  diagnosis. 

A  friend  told  me  he  painted  a  pea-green  lion  for 
his  little  boy.  Another  wore  a  green  and  a  brown 
glove.  A  young  architect  put  a  green  roof  on  a 
church,  and  was  indisposed  to  admit  having  made 
any  mistake.  Complaints  to  me  from  the  color- 
blind, as  to  the  colors  of  horse-cars  by  day  and 
their  lights  by  night,  have  been  very  frequent. 
A  medical  friend  tells  me  that  on  a  yacht  he  must 
have  a  piece  of  red  glass  marked  red^  and  green 
marked  green^  to  look  at,  to  endeavor  to  impress 
on  liis  eye  the  sensation,  and  compare  it  with  the 
red  or  green  light  of  an  approaching  vessel.  His 
matches  of  worsted  were  amusing,  and  showed 
complete  red-blindness.  I  happened  to  meet  him 
on  the  street ;  and,  on  questioning  him,  I  found  he 
could  see  no  color  in  a  bright-red  express-wagon,  a 
brilliant  new  scarlet  "  soldier's  messenger  "  cap,  nor 
could  he  distinguish  a  lad  by  his  deep-red  scarf. 
His  brother  was  nearly  the  same.  Yellow-stained 
glass  in  a  door  they  recognized,  but  thought  pale 
green  was  white,  or  "  the  color  of  soda-water." 

As   has  been  truly  said,  "  Volumes  might  be 


20  COLOR-BLINDNESS  : 

written  on  this  subject  if  the  different  instances 
of  all  the  peculiarities  presented  by  color-blindness, 
and  all  the  embarrassment  to  which  they  give  rise, 
were  cited." 

The  question  of  correctly  distinguishing  colors 
comes  up  in  a  practical  form  more  often  than  we 
imagine  in  every-day  life.  Such  articles  as  the 
following,  clipped  from  the  newspapers  of  a  day, 
attract  naturally  the  attention  only  of  those 
specially  interested  in  or  investigating  color-per- 
ception :  — 

"  New  Bedford,  Aug.  30.  —  Masters  of  vessels  arriving 
at  Vineyard  Haven  complairK,  that,  since  the  red  light  at  the 
East  Chop  has  been  removed  to  the  new  tower  built  for  it, 
it  is  scarcely  distinguishable  from  the  West  Chop,  or  any 
other  fixed  white  light.  The  captain  of  schooner  '  Hanni- 
bal,' of  Islesborough,  Me.,  made  it  on  Saturday  evening,  ap- 
proaching from  the  eastward,  in  thick  weather,  and  called  it 
West-Chop  light,  and  changed  his  course  to  run  in  Yineyard- 
Haveu  Harbor,  and  just  escaped  running  ashore  near  Oak 
Bluffs  by  making  the  light  at  that  place  through  the  fog. 
Such  accidents  as  the  above  can  only  occur,  however,  in 
thick  weather,  when  but  one  of  the  two  lights  on  the  Chops 
of  the  harbor  can  be  seen  at  the  same  time." 

"  An  English  inventor,  J.  J.  Nickoll,  has  brought  out  a 
system  of  helm-signals.  In  describing  his  invention  to  the 
Inventors'  Institute,  Mr.  Mckoll  says,  '  As  my  signals  move 
automatically  with  the  rudder,  every  material  shifting  of 
the  helm  to  the  port  or  starboard  is  at  once  shown  at  the 
head  of  the  vessel  by  a  red  or  green  light,  and  before  she 
answers  her  helm,  thus  giving  timely  notice  to  an  approach- 
ing ship  what  course  she  is  about  to  steer.  The  signals  act 
independently  of  the  regulation  mast-head  lights.'  " 

As  if  the  present  necessary  marine-signals  were 
not  difficult  enough  to  read  quickly,  a  writer  in 
"  The  Scientific  American "  proposes  that  there 
should  be  exhibited  a  red  light  for  north,  green  for 


ITS   DANGERS   AND    ITS   DETECTION.  21 

south,  yellow  for  east,  and  white  for  west.  When 
steering^  clue  north  a  red  liojht  is  to  be  shown; 
when  steering  north-north-east  one  light  under 
this;  north-east  two  lights;  east-north-east  three 
lights,  &c. ;  and  so  on  for  the  other  points  of  the 
compass.  Every  change  of  course  is  to  be  imme- 
diately followed  by  a  change  of  these  lanterns. 
Such  a  proposal  but  expresses  the  general  laqk 
of  appreciation  of  the  difficulties  with  all  night- 
signals. 

'•  The  Eastern  Railway  Company  has  recently  placed 
upon  the  whole*  route  of  its  line  patent  switches  painted 
red,  with  an  index  pointing  across  the  track  if  all  is  not 
right.  At  night  a  green  lantern  signifies  the  track  is  clear, 
and  a  red  one  if  not.  The  company  claims  that  by  this 
simple  arrangement  accidents  will  not  be  of  so  frequent 
occurrence  as  under  the  old  system  of  signals." 

A  post-office  clerk  in  Prussia  was  found  to  be 
constantly  in  trouble  with  the  stamps.  The  ac- 
counts would  come  wrong.  Sometunes  there  was 
not  enough  money  in  return  for  stamps  sold  ;  and 
on  other  occasions  there  was  too  much.  This 
made  dishonesty  on  his  part  less  likely;  but  it 
was  incomprehensible  how  he  would  make  the 
accounts  so  entanHed.  At  lencr-th  it  was  dis- 
covered  that  he  was  color-blind,  and  could  not 
distinguish  red  from  green  stamps  ("  Boston 
Medical  and  Surgical  Journal,"  Dec.  27,  18T7). 
No  doubt  letters  in  the  United  States  find  their 
way  to  the  Dead-Letter  Office  as  unpaid  from  the 
color-blind  senders  putting  on  red  two-cent  instead 
of  green  three-cent  stamps,  since  we  all,  from  habit, 
regard  the  color  rather  than  the  number  on  a 
postage-stamp,  especially  when  in  haste. 


22  COLOK-BLINDNESS 


CHAPTER  III. 

FOEMER   CLASSIFICATION  OF   THE  COLOE-BLIND. 

By  this  long  list  of  reports  from  the  examiners 
or  the  examined,  I  have  not  only  enabled  my  read- 
ers to  recognize  what  are  the  mistakes  the  color- 
blind make,  but  also,  perhaps,  assisted  them  in 
grouping  into  certain  classes  those  with  this  chro- 
matic defect.  This,  as  will  be  seen,  is  of  impor- 
tance ;  but  it  was  not  done  till  1837  by  Professor 
Seebeck.  Of  course  any  one  observer  of  this 
then  simply  scientific  curiosity  had  hardly  oppor- 
tunity of  comparing  any  great  number  of  cases' 
together,  and  thereby  deducing  some  laws  con- 
cerning them,  or  sorting  out  the  color-blind  into 
classes  according  to  their  special  form  of  trouble. 
Seebeck  personally  investigated  a  number  for  that 
time  very  large,  —  namely,  twelve  cases ;  and  he 
was  the  first  to  work  philosophically,  recognizing 
and  insisting  on  the  uselessness  of  asking  the  color- 
blind the  color-names  of  objects.  Pie  proved  the 
importance  of  letting  them  show  their  own  com- 
parisons by  having  a  number  of  colored  objects 
mixed  up  together,  and  allowing  them  to  select 
and  group  together  those  which  seemed  to  them 


ITS   DAXGEES  AND   ITS  DETECTION.  23 

of  the  same  color.  He  had  some  three  hundred 
pieces  of  varionsly  colored  paper,  also  variously 
colored  pieces  of  glass.  He  recommends  worsteds, 
but  thinks  silks  would  be  too  brilliant.  He  did  not 
use  worsteds,  but  did  employ  the  spectrum  and 
polarized  light  in  addition  to  the  test  with  the 
colored  papers,  &c. 

His  deductions  were,  that  there  was  a  class  of 
color-blind  who  seemed  quite  insensible  to  the  spe- 
cific impression  of  all  colors,  —  most  so  for  red  and 
naturally,  also,  its  complementary  green^  in  that 
they  could  distinguish  them  but  little,  if  any,  from 
gray ;  then  for  blue,  which  they  did  not  well  sepa- 
rate from  gray.  Their  sensation  of  yellow  seemed 
best  developed,  though  this  did  not  appear  so  differ- 
ent from  colorless  as  to  a  normal  eye.  Such  per- 
sons more  or  less  confounded  bright  orange  and 
pure  yellow;  deep  orange,  bright  yellowish  or 
brownish  green,  and  yellowish  brown ;  pure  bright 
green,  grayish  brown,  and  flesh-color ;  rose-red, 
green  (rather  bluish  than  yellowish),  and  gray ; 
carmine,  dark  green,  and  hair-brown ;  bluish  green 
and  impure  violet;  lilac  and  bluish  gray;  sky- 
blue,  grayish  blue,  and  grayish  lilac. 

Another  class  he  found  very  similar  to  the  first. 
They  also  recognize  yellow  best,  and  distinguish 
red  better,  blue  rather  less  from  colorless,  but 
especially  confound  red  and  blue.  The  colors 
they  confound  with  each  other  are  clear  orange, 
greenish  yellow,  brownish  yellow,  and  pure  yel- 
low; bright  orange,  yellowish  brown,  and  grass- 
green  ;  sealing-wax  red,  rusty  brown,  and  dark  olive 
green;  cinnabar-red  and  dark  brown;  dark  car- 
mine red  and  dark  bluish  green;   flesh-red,  gray 


24  COLOR-BLINDNESS  : 

brown,  and  blue   green;   pale  bluish   green   and" 
gray  (rather  brownish)  ;  impure  rose  (rather  yel- 
lowish) and  pure  gray ;  rose-red,  lilac,   sky-blue, 
and   gray   (towards   lilac);    carmine   and  violet; 
dark  violet  and  dark  blue. 

Seebeck  was  the  first,  besides  grouping  the  color- 
blind into  classes,  to  show  also  that  there  were 
degrees  of  this  trouble  as  varying  as  the  visual 
poWer  for  form,  which  we  now  recognize  as  indi- 
vidual. 

Again,  from  an  analysis  of  our  long  list  of  re- 
ported difficulties  with  chromatic  vision,  we  may 
see  how  it  was,  from  a  study  of  all  the  then  ac- 
cessible cases,  Szokalski  distinguished  five  classes 
of  color-blind, — 

1.  That  of  j)ersons  in  whom  the  sense  of  colors  is 
almost  completely  wanting,  and  who,  in  place  of 
the  elementary  colors, — yellow,  red,  and  blue, — 
see  only  different  degrees  of  white  and  black. 

2.  That  of  persons  who  also  distinguish  yel- 
lows: external  objects  appear  to  them  colored 
with  shades  which  generate  the  different  mixtures 
of  yellow,  of  white,  and  of  black. 

3.  That  of  persons  who,  besides  seeing  yellow, 
have  a  common  perception  for  both  blue  and  red. 

4.  That  of  pers(5ns  destitute  solely  of  the  per- 
ception of  red,  which  appears  to  them  ash-gray. 

5.  That  of  individuals  who  distinguish  all  col- 
ors, but  not  in  a  decided  manner :  instead  of  being 
able  to  distinguish  the  mixture  of  two  colors,  they 
never  see  but  one  of  them. 

Professor  Purkinje,  again,  from  an  analysis  of 
cases  observed  and  then  recorded,  divides  color- 
blindness into  four  varieties.     The  first  two  re- 


ITS  DANGERS  AND  ITS  DETECTION.  25 

late  more  to  the  intensity,  the  others  to  the  na- 
ture, of  the  imperfection. 

Professor  Elie  Wartman,  writing  in  1840,  says,  — 

"  The  various  ancient  and  recent  obseryations  which  I 
have  to  relate  appear  to  me  to  confirm  the  division  of  See- 
beck,  rather  than  that  of  Szokalski  and  Purkinje.  It  would 
be  very  advantageous  to  make  a  strict  classification  of  the 
color-blind,  because  for  each  category  means  might  be  of- 
fered at  once  simple  and  few  as  palliatives  of  their  imper- 
fections. Unhappily  such  an  undertaking  does  not  seem 
possible,  and  we  may  say  that  there  are  as  many  varieties  of 
color-blindness  as  of  individuals  who  are  affected  with  it. 
With  regard  to  the  very  rational  distinction  which  Seebeck 
has  the  merit  of  having  first  established  between  the  errors 
of  appreciation  of  intensihj,  and  those  of  judgment  of  the  in- 
dividual Jdnd  of  colors,  it  is  to  be  regretted  that  we  cannot 
make  it  in  the  great  majority  of  the  descriptions  which  writ- 
ers have  transmitted  to  us.  I  prefer  only  to  separate  the 
cases  of  dichromatic  and  pobjcliromatic  color-blindness ;  that 
is  to  say,  where  there  are  more  than  two  colors  perceived 
normally." 

I  have  thus  briefly  given  the  earlier  attempts  to 
classify  the  color-blind,  that  the  difficulty  of  so 
doing  may  be  recognized.  We  shall  also  thus  be 
better  able  to  appreciate  the  value  of  the  applica- 
tion of  the  theory  for  this  purpose  described  in 
the  next  chapter. 


26  COLOE-BLINDNESS 


CHAPTER  IV. 

PRESENT  CLASSIFICATION  OF  THE  COLOE-BLIND 
IN  ACCORDANCE  WITH  THE  YOUNG-HELMHOLTZ 
THEORY   OF   COLOR-PERCEPTION. 

A  PROPER  division,  and  a  consequent  correct 
understanding,  of  color-blindness  was  not  made 
till  this  half  of  our  century.  Professor  Helm- 
holtz  brought  forward  the  long-forgotten  work  of 
Thomas  Young,  and  applied  his  theory  of  color- 
perception  to  the  results  of  more  modern  investi- 
gations, with  the  final  development  of  what  is  now 
called  the  Young-Helmholtz  theory  of  color-sense. 
Helmholtz  says,  — 

"A  reduction  of  colors  to  three  base  colors  has  only  a 
subjective  meaning :  it  is  but  reducing  or  carrying  back  the 
sensations  of  color  to  three  base  or  final  sensations.  In  this 
view  Thomas  Young  correctly  grasped  the  problem,  and,  in 
fact,  his  theory  gives  us  a  very  simple  and  clear  view  and 
explanation  of  all  the  phenomena  of  the  physiology  of  color. 
Thomas  Young  holds  that,  — 

"1.  There  are  in  the  eye  three  kinds  of  nerve-fibres. 
Stimulation  of  the  first  produces  the  sensation  of  red,  tlie 
second  that  of  green,  and  of  the  third  the  sensation  of  violet. 

"2.  Objective  homogeneous  light  excites  these  three 
kinds  of  fibres  in  varying  degree  according  to  the  wave- 
lengths.    The  red  perceptive  fibres  will  be  strongest  stimu- 


ITS   DANGERS   AND   ITS   DETECTION. 


27 


lated  by  light  of  the  greatest  wave-length,  the  green  per- 
ceptive by  light  of  medium  wave-length,  and  the  violet 
perceptive  by  light  of  the  smallest  wave-length.  Here  must 
not  be  excluded,  but  rather  accepted  in  explanation  of  a 
series  of  phenomena,  that  each  spectral  color  excites  all 
three  kinds  of  fibres,  —  but  one  less,  the  others  more  strong- 
ly. Let  us  suppose,  as  in  Fig.  1,  the  spectral  colors  in  a 
horizontal  row  from  red  to  violet :  then  the  three  curves  will 
represent  the  intensity  of  stimulation  of  the  three  kinds  of 
fibres,  —  (1)  the  red  perceptive ;  (2)  the  green  perceptive ; 
and  (3)  the  violet  perceptive  elements  or  fibres. 


"  Simple  red  strongly  stimulates  the  red  perceptive,  less 
the  other  two  :  sensation,  red. 

"  Simple  yellow  stimulates  moderately  the  red  and  green 
perceptive,  feebly  the  violet :  sensation,  yellow. 

"  Simple  green  stimulates  strongly  the  green  perceptive, 
much  less  the  other  two  :  sensation,  green. 

"  Simple  Mue  stimulates  moderately  the  green  and  violet 
perceptive  fibres,  feebly  the  red  :  sensation,  blue. 

"  Simple  violet  stimulates  strongly  the  violet  perceptive, 
feebly  the  other  fibres  :  sensation,  violet. 

"Equally  strong  stimulation  of  all  the  fibres  gives  the 
sensation  of  white  or  whitish  colors." 

This  is  not  the  place  to  discuss  the  Young- 
Helmholtz  theory  of  color-perception.  It  must  be 
remembered  that  the  facts  in  relation  to  color- 
blindness given  in  this  volume  are  not  collected 
in  support  of  any  theory,  iior  is  any  theory  argued 
for.  The  Young-Helmholtz  is  used  rather  as  a 
means   of  better  explaining  this  defect.     It  will 


28  COLOR-BLINDNESS  : 

assist  our  understanding  its  relations  to  color- 
blindness to  read  Helmholtz's  explanatory  intro- 
duction of  it :  — 

'' Perhaps  there  will  be  much  objection  to  this  hypothe- 
sis, from  the  number  of  the  necessary  nerve-fibres  or  nerve- 
terminations  being  tripled,  in  comparison  with  the  common 
theory,  where  every  individual  nerve  carries  all  possible 
color-stimulations.  I  do  not  think,  however,  that  in  this 
respect  Young's  theory  is  in  opposition  to  anatomical  facts, 
since  we  know  nothing  of  the  number  of  the  transmitting 
fibres ;  and  then,  besides,  there  are  a  number  of  microscopic 
elements  present,  whose  special  function  we  do  not  as  yet 
know.  Moreover,  this  is  not  the  most  essential  in  Young's 
hypothesis.  That  seems  to  me  to  be  rather  the  j)resenting 
color-sensations  as  composed  of  three  wholly  independent 
actions  in  the  nerve-substance.  It  is  not  absolutely  neces- 
sary to  suppose  separate  nerve-fibres  for  these  separate  sen- 
sations. The  same  value  of  Young's  hypothesis  in  this  ex- 
planation is  shown,  if  we  suppose  that  in  each  individual 
fibre  three  different  and  independent  actions  may  take  place. 
Since,  however,  the  form  of  the  hypothesis,  as  originally 
proposed  by  Young,  is  capable  of  more  definite  presenta- 
tion and  expression  than  such  a  modification  of  it  would 
allow,  we  will,  in  view  of  its  description,  retain  the  original 
plainer  form.  Moreover,  the  physical  phenomena  of  nerve- 
stimulation —  namely,  the  electro-motor  —  are  not  marked  in 
the  sensitive  or  motor  nerves  by  such  a  variation  in  action 
as  would  necessarily  be  the  case  if  each  nerve-fibre  trans- 
mitted all  color-sensations.  By  Young's  hypothesis  we  may 
also  apply  to  the  optic  nerve  the  simple  conceptions  of  the 
mechanism  of  stimulation  and  conduction  which  we  have  de- 
rived from  the  study  of  the  phenomena  in  the  motor  nerves. 
This  we  could  not  do  if  we  must  admit  that  each  optic 
nerve-fibre  is  to  have  three  qualitatively  different  conditions 
of  stimulation  without  mutual  interference.  Young's  hy- 
pothesis is  only  a  more  special  carrying-out  of  the  law  of  the 
specific  energies  of  the  senses.  As  the  sense  of  touch,  and 
the  sense  of  sight  in  the  eye,  have  evidently  separate 
nerve-fibres,  so  is  the  same  claimed  for  the  sensation  of  the 
several  base  colors.     The  choice  of  the  three  colors  is  some- 


ITS   DANGERS   AND   ITS   DETECTION.  29 

what  arbitrary.  Any  three  colors  could  have  been  taken 
whose  combination  produced  white  light.  So  far  as  I  see 
at  present,  there  is  no  other  means  of  determining  the  base 
colors  than  the  examination  of  the  color-blind." 

For  further  description  of  the  Yoiing-Helmlioltz 
theory  of  color-perception  I  would  refer  the 
reader  to  Helmholtz's  popular  scientific  lectures. 
I  have  given  above  the  essential  points,  as  this 
was  necessary  to  enable  us  to  readily  follow  out 
the  application  of  the  theory  thus  stated  by  Helm- 
holtz  to  the  condition  of  the  color-blind.  By 
Young's  theory  Helmholtz  has  shown  how  colors 
must  appear  to  the  color-blind.  This  has  been, 
however,  so  well  extended  and  explained  in  Pro- 
fessor Holmgren's  book,  that  I  cannot  do  better 
than  quote  from  it  here.  In  deference  to  the 
Smithsonian  Institute  I  will  give  their  translation 
rather  than  my  own.  Professor  Holmgren  goes 
on  to  say,  — 

"  These  curves  (Fig.  1)  enable  us  to  explain  easily  the 
colors  of  the  spectrum  by  the  theory.  We  find  in  what  pro- 
portion each  one  of  the  three  fundamental  perceptions  en- 
ters into  it  by  measuring  the  vertical  distance  from  their 
place  on  the  horizontal  line  (abscissa)  to  the  corresponding 
points  of  each  of  the  three  curves.  It  is  then  seen  that 
there  is  no  color  of  the  spectrum  into  which  but  one  primi- 
tive color  enters  exclusively.  The  two  others  also  furnish 
their  contingent.  No  one  is  therefore  perfectly  "  saturated." 
They  are  more  or  less  spread  with  white,  and  green  is  the 
least  sensibly  "  saturated,"  or  more  whitish.  The  curves 
also  show  us  that  yellow  and  blue  are  at  the  same  time 
whitish  colors,  and  the  most  intensely  luminous  in  the  whole 
spectrum.  When  we  again  add  that  a  color,  "  saturated  "  in 
almost  the  same  degree  as  the  other  spectral  colors,  pro- 
ceeds from  the  homogeneous  combination  of  red  and  violet, 
—  that  is  to  say,  purple,  and  its  whitish  shade,  pink,  — we 
shall  have  said  all  theoretically  that  we  have  to  say  in 
relation  to  the  normal  chromatic  sense. 


30  COLOE-BLINDNESS  : 

"  To  explain  the  abnormal  sense  of  colors  by  the  theory 
of  the  normal,  we  can,  in  advance,  conceive  various  possi- 
bilities. Let  tis  suppose  that  one  of  the  three  fundamental 
perceptions  is  wanting,  or  that  one  of  the  primitive  colors  is 
absent :  it  is  clear  that  the  whole  chromatic  system  will  be 
upset.  It  is  evident,  therefore,  that  this  system  must  be 
completely  different,  according  to  the  absence  of  one  or  the 
other  of  the  three  primitive  colors.  It  is  virtually  just  in 
this  way  that  it  has  been  attempted  to  exi3lain  cases  of  a 
strongly  marked  defect  in  the  chromatic  sense,  or  genuine 
types  of  blindness  to  color,  found  in  real  life.  The  term 
color-blindness  has  been  justified  by  this,  as  it  indicates  in 
each  case  a  genuine  blindness  to  one  of  the  primary  colors. 
In  this  way,  therefore,  we  distinguish,  according  to  the  kind 
of  element  wanting,  three  classes  of  blindness,  — 

"  1st,  Red-blindness. 

"  2d,  Green-blindness. 

"3d,  Violet-blindness. 

"  We  shall  see  that  the  Young-Helmholtz  theory,  far  from 
being  contradicted,  as  has  been  recently  claimed,  by  the 
phenomenon  of  color-blindness,  finds  in  it,  on  the  contrary, 
a  support;  and  this  theory  most  certainly  furnishes  the  best 
guide  for  attaining  the  practical  end  in  view  for  which  we 
intend  to  use  it.  Let  us,  in  the  first  instance,  cast  a  rapid 
glance  over  the  different  kinds  of  typical  and  complete 
blindness  to  colors  as  their  features  are  presented  by  the 
theory.  This  sketch  will  be  singularly  facilitated  by  the  use 
of  the  same  kind  of  curves  employed  in  illustrating  the 
normal  sense  of  colors. 

"  1.  According  to  the  theory,  blindness  to  red  is  due  to  the 
absence  or  paralysis  of  the  organs  perceiving  red  (Fig.  2). 
Red-blindness  has,  then,  but  two  fundamental  colors,  which, 
adhering  strictly  to  the  theory,  are  green  and  violet  (blue 
according  to  Maxwell). 

"  The  curves  distinctly  show  what  aspect  the  various 
kinds  of  lights  of  the  spectrum  must  have  for  the  chromatic 
sense,  such  as  the  one  we  have  in  view.  We  will  give  a 
short  list  of  them,  according  to  Helmholtz,  by  designating 
here  the  different  kinds  of  lights,  —  by  using  terms  borrowed 
from  the  impressions  they  produced  on  the  normal  chromatic 
sense.     The  comparison  will  not  be  without  interest:  — 


ITS   DANGERS   AND  ITS   DETECTION. 


31 


" '  Spectral  red,  ^Yhich  feebly  excites  the  perceptive  organs 
of  green^  and  scarcely  at  all  those  of  violet,  must  conse- 
quently appear  to  the  red-blind  a  '''•saturated  "  green  of  a  fee- 
hie  intensiti/,  more  "  saturated  "  than  normal  green,  into  which 
a  sensible  portion  of  the  other  primitive  colors  enters. 
Feebly  luminous  red,  which  affects  the  perceptive  organs  of 
red  in  a  normal  eye  sufficiently,  does  not,  on  the  other  hand, 
sufficiently  excite  the  perceptive  organs  of  green  in  the  red- 
blind  ;  and  it  therefore  seems  to  them  black.  Spectral  yel- 
low seems  to  them  a  green  ^•saturated"  and  intensely  luminous ; 
and,  as  it  constitutes  the  precisely  saturated  and  very  intense 
shade  of  that  color,  it  can  be  understood  how  the  red-blind 
select  the  name  of  that  color,  and  call  all  those  tints  that 
are,  properly  speaking,  green,  yellow.  Green  shows,  as  com- 
pared with  the  preceding  colors,  a  more  sensible  addition  of 


the  other  primitive  colors :  it  then  appears,  consequently, 
like  a  more  intense  but  whitish  shade  of  the  same  color  as 
yellow  and  red.  The  greatest  intensity  of  light  in  the  spec- 
trum, according  to  Seebeck's  observations,  does  not  appear 
to  the  red-blind  to  be  in  the  yell-ow  region,  as  it  does  to  the 
normal  eye,  but  rather  in  that  of  the  blue  green.  In  reality, 
if  the  excitation  of  the  perceptive  organs  of  green,  as  it  was 
necessary  to  assume,  is  strongest  for  green,  the  maximum  of 
the  total  excitation  of  the  red-blind  must  be  found  slightly 
toward  the  blue  side,  because  the  excitation  of  the  organ 
perceiving  violet  is  then  increased.  The  white  of  the  red- 
blind  is  naturally  a  combination  of  their  two  primitive  colors 
in  a  determinate  proportion,  —  a  combination  which  appears 
blue  gray  to  the  normal  sight :  this  is  why  he  regards  as 
gray  the  spectral  transition  colors  from  green  to  blue. 
Then  the  other  color  of  the  spectrum,  which  they  call  hlue^ 
preponderates,  because  indigo-blue,  though  somewhat  whit- 


32  COLOE-BLINDNESS  : 

ish  according  to  their  chromatic  sense,  is  to  them,  owing  to 
its  intensity,  a  more  evident  representative  of  that  color  than 
violet.' 

"  This  description  of  the  manner  in  which  the  red-blind 
forms  a  conception  of  the  different  kinds  of  light  of  the 
spectrum  is  assuredly  a  conclusion  logically  deduced  from 
the  theory ;  but  it  accords  so  well,  at  the  same  time,  with  the 
experience  acquired  in  examining  the  color-blind,  that  this 
might  perfectly  serve  -to  support  and  corroborate  the  theory. 
We  will  simply  add  a  point  for  our  especially  practical  pur- 
pose, or  rather  emphasize  one  point  of  this  theory.  In  fact, 
it  is  clear  that  a  red  and  a  green  light  especially  excite  one 
and  the  same  element  in  the  red-blind.  A  ray  red  and 
green,  or  an  object  red  and  green,  to  the  normal  sense,  must 
seem  fundamentally  to  the  red-blind  to  be  the  same  color; 
and  if,  in  especial  cases,  he  knows  how  to  discriminate,  his 
judgment  is  simply  guided  by  the  intensity  of  the  light. 
The  intensity  of  light  is  much  more  feeble  (as  shown  by 
Fig.  2)  in  red  than  in  green.  If,  then,  a  red-blind  individual 
finds  that  a  red  and  a  green  tint  are  exactly  alike,  it  is  neces- 
sary that  the  green  be  to  the  normal  eye  much  less  intense 
than  the  red.  This  is  distinctly  shown  by  the  vertical  dot- 
ted lines  between  R.  and  O.,  and  also  between  Y.  and  G., 
in  Fig.  2 ;  and  this  is  entirely  confirmed  by  experience, 

"  2.  Green-blindness  derives  its  origin,  according  to  the 
theory,  from  the  absence  or  paralysis  of  the  perceptive  ele- 
ments of  green.  The  green-blind  has  therefore  but  two 
fundamental  colors ;  that  is,  —  still  closely  adhering  to  the 
theory,  —  red  and  violet  (blue  according  to  Maxwell).  The 
spectrum  for  green-blindness  should  be,  according  to  the 
theory,  constructed  in  the  following  manner :  — 

"  The  spectral  red,  which  strongly  excites  the  perceptive 
organs  of  red,  and  but  very  faintly  those  of  violet,  must 
therefore  appear  to  the  green-blind  as  an  extremely  '  satu- 
rated '  red,  but  of  a  light  somewhat  less  intense  than  the 
normal  red,  which  is  comparatively  more  yellowish,  as  green 
forms  a  part  of  it.  The  spectral  orange  is  again  a  very 
'saturated'  red,  but  much  more  luminous.  Yellow  is  un- 
doubtedly a  more  intensely  luminous  red  than  the  spectral 
red,  but,  on  the  other  hand,  more  whitish,  because  a  sensible 
portion  of  the  other  primitive  color  enters  into  it. 


ITS   DANGERS   AND   ITS   DETECTION. 


33 


"  Green,  with  its  shades  inclining  to  yellow  and  blue, 
ought,  correctly  speaking,  to  be  a  'saturated'  purple,  and 
with  a  mean  intensity  of  light :  but  it  is  the  white  (gray)  of 
the  green-blind;  for  it  is  composed  of  almost  equal  parts 
of  the  two  primitive  colors. 

"  The  blue  is  an  intense  violet,  but  a  little  less  '  saturated ' 
than  indigo,  which  is  more  strongly  luminous  and  more 
'saturated.'  A^iolet  is  a  little  less  intense,  but  more  'satu- 
rated '  than  normal  violet.  The  tints  most  luminous,  and  at 
the  same  time  most  '  saturated,'  which  must  constitute  the 
types  of  the  j^rimitive  colors  of  the  green-blind,  are  orange 
(or  its  immediate  neighbor  in  the  spectrum,  red)  and  indigo- 
blue.  Now,  orange  is  a  color  which,  in  ordinary  language, 
especially  amongst  the  uncultivated  and  unpractised,  is  in- 
discriminately called  red  and  yellow  :  this  fact  explains  why 
the  green-blind  denominate  their  first  primary  color  some- 


FlG, 


times  'red 'and  sometimes  'yellow.'  We  will  add  to  this 
description  the  same  remark  made  about  red-blindness.  In 
green-blindness  the  same  organ  is  also  found  affected  by 
spectral  red  and  green  light.  Red  and  green  are  then  per- 
ceived by  the  green-blind  in  the  same  way,  or,  in  other 
words,  are  to  Mm  in  fact  exactly  the  same  color.  In  cases 
where  he  succeeds  in  distinguishing  them,  it  is  by  the  aid  of 
the  intensity  of  the  light;  but,  with  regard  to  this  intensity 
of  light,  it  is  the  opposite  of  what  occurs  in  the  case  of  the 
red-blind.  A  green  tint  which  to  the  green-blind  must  ap- 
pear exactly  like  a  red  one,  to  a  normal  sense  of  color  must 
be  sensibly  more  luminous  than  red.  This  is  shown  by  the 
dotted  vertical  lines  between  R.  and  O.,  and  also  between 
Y.  and  G.  (Fig.  3),  and  is  confirmed  in  every  res]3ect  by 
experience. 

"  Violet-blindness  (or  blue  according  to  Maxwell)  is  due, 


34 


COLOE-BLINDNESS 


according  to  the  theory,  to  the  absence  or  paralysis  of  the 
elements  perceiving  violet.  The  two  primitive  colors  of  the 
violet-blind  are  then,  according  to  theory,  red  and  green. 
The  spectrum  of  the  violet-blind  must,  in  consequence,  be 
represented  as  follows  :  — 

"  The  red  is  a  purer  red  color  (not  yellowish)  than  normal 
red,  but  still  less  '  saturated.'  The  more  it  inclines  toward 
orange,  the  more  strongly  luminous  it  is,  but  is  at  the  same 
time  less  *  saturated,'  more  whitish.  The  yellow  is,  as  it 
were,  a  combination  of  almost  equal  proportions  of  the 
fundamental  colors  that  form  white.  Green  is  a  strongly 
luminous  but  whitish  green,  which,  in  tending  toward  the 
blue,  becomes  more  and  more  '  saturated ;  '  so  that  greenish 
blue  must  be  the  type  of  these  hues.  The  blue  is  a  green  of 
moderate  luminosity,  and  strongly  '  saturated ; '  and  violet  is 
green  very  feebly  luminous,  but  also  '  saturated  '  in  a  much 


higher  degree  than  the  normal.  A  violet  strongly  luminous 
is  sufficient  to  induce  this  green ;  but  a  feeble  violet,  although 
very  sensible  to  the  normal  eye,  is  black  to  the  color-blind 
in  question. 

"  It  is  plain  that  the  violet-blind,  whose  primitive  colors 
are  red  and  green,  do  not  confuse  these  colors.  This  kind 
of  blindness,  from  the  experiments  made  so  far,  must  be 
very  rare.  For  our  part  we  have  not  succeeded  in  discover- 
ing more  than  two  cases  agreeing  quite  exactly  with  the 
description  given  by  the  theory;  while  the  first  two  kinds 
are  comparatively  very  common.  In  order  to  be  abnormal 
it  is  not  necessary  that  a  sense  of  color  should  completely 
fulfil  the  conditions  indicated  in  the  types  we  have  just 
described.  We  might  perfectly  conceive  a  resultant,  not  of 
an  absolute  absence  or  of  a  complete  paralysis  of  one  kind 
of  perceptive  elements,  but  solely  of  a  comparatively  very 


ITS   DANGERS   AXD   ITS   DETECTION.  35 

low  excitability,  or,  if  preferred,  of  a  much  more  limited 
number  of  one  kind  of  elements,  acting  on  the  retina,  as 
compared  with  the  two  other  kinds.  It  is  very  easy  to  con- 
struct curves  in  conformity  with  this  idea,  and  not  less  easy 
to  arrange  in  this  manner  a  continuous  series  of  transitions 
and  gradual  forms  between  one  kind  of  complete  color-blind- 
ness on  one  side  and  the  normal  chromatic  sense  on  the 
other.  This  kind  of  defective  vision  might  be  called  incom- 
plete color-hlindness,  to  distinguish  it  from  complete,  as  we 
have  just  characterized  the  three  different  kinds.  Our  expe- 
rience has  taught  us  that  the  intermediary  forms  agreeing 
with  the  data  given  above  are  met  in  large  numbers  in  prac- 
tice, and  of  very  different  degrees.  These  are  the  forms  we 
designated  under  the  common  appellation  of  incomplete  color- 
blindness; but  we  can,  according  to  the  theory,  still  conceive 
other  forms  of  a  defective  sense  of  color.  There  is  one, 
amongst  others,  which  has  at  command  only  one  of  the 
three  kinds  of  elements.  Such  a  sense  of  sight  is  not  prop- 
erly a  chromatic  sense.  For  it  there  exists  no  specific  dif- 
ference in  light;  that  is  to  say,  no  color.  Every  kind  of  light 
here  acts  as  if  on  one  element  alone.  This  is  why  the 
single  perception  of  differences  of  intensity  of  light  (quan- 
tity), but  not  of  differences  of  color  (quality),  is  possible. 
This  condition  may  then  be  designated  under  the  name  of 
total  color-blindness.  Several  cases  have  been  mentioned 
from  time  to  time ;  but  we  have  not  succeeded  in  finding  a 
single  one,  and  it  may  well  be  questioned  whether  such  a 
case   has   actually   existed.^      We  may  also   conceive  that 

1  l^ofessor  Bonders  reported  an  interesting  case  of  congenital  total  color- 
blindness at  the  Heidelberg  Ophtbalmological  Society  1871 :  An  educated 
young  man  of  twenty-one  years  of  age  was  totally  color-blind.  Strong  light 
blinded  him  :  in  moderate  light  he  saw  very  well.  He  was  myopic  one-eighth, 
and  read  for  hours  without  glasses.  Out  of  doors,  all  glasses  which  absorbed 
light,  without  difference,  —  even  the  brightest  colored  ones,  — were  pleasant  to 
him,  because  they  reduced  the  light.  In  the  dioptric  spectrum  of  a  gas-lamp 
his  brightest  part  was  between  the  spectral  lines  D  and  E,  close  to  E  :  hence 
in  greenish  yellow.  From  here  outwards  towards  the  red  end  the  light  faded 
rapidly ;  towards  the  violet,  at  first,  slowlj-,  then  rapidly.  By  moderate  il- 
lumination he  lost  less  of  the  brightest  of  the  spectrum  on  this  side  than 
towards  the  red  end.  With  the  polariscope,  the  complementary  colors 
"hrough  the  quartz  plate  appeared  to  him  of  the  same  color.  In  turning  the 
double-refractive  prism  he  had  a  maximum  of  brightness  at  every  ninety 
degrees,  or  equaUty  of  brightness,  as  if  the  quartz  plate  was  not  there.  He 
had  the  greatest  difference  when  Bonders  himself  saw  purple  and  green; 
equality,  when  he  saw  yellow  and  blue.  Trials  were  also  made  with  Che- 
vreul's  chromatic  circle. 


36 


COLOR-BLINDNESS 


another  form  of  a  defective  sense  of  color  arises  from  the 
three  kinds  of  elements  being  uniformly  of  moderate  sensi- 
bility. We  are  able  to  trace  the  following  diagram  (Fig.  5), 
by  which  the  three  curves  simultaneously  approach  the  ab- 
scissa, or  horizontal  line,  and  are  flattened  in  such  a  manner 
that  the  vertices  disappear  the  first. 

"  As  is  readily  observed,  green  is  then  precisely  the  color, 
which,  being  ordinarily  the  most  whitish  of  the  primitive 
colors,  is  the  first  to  lose  its  quality  of  'saturated'  color, 
and  shades  into  gray.  This  must  then  be  the  exact  scheme 
of  pathological  color-blindness,  according  to  the  theory.  In 
fact,  we  have  found  in  our  examinations  a  large  number 
of  cases  perfectly  harmonizing  with  this  scheme.  We  have 
therefore  classed  them  under  the  head  of  incomplete  color- 
blindness;  and  this  from  essentially  practical  reasons.  To 
define  their  nature  according  to  the  theory,  it  is  necessary 


to  regard  them  as  a  particular  variety,  which  we  shall  call 
Si  feeble  sense  of  colors.  We  are  not  of  course  able  to  decide 
how  far  defects  of  this  kind  should  be  considered  as  having 
a  pathological  origin,  or  whether  they  are  ever  congenital. 
For  this  determination  a  much  wider  experience  in  this  par- 
ticular department  than  we  now  possess  is  requisite,  for  rea- 
sons to  be  given  hereafter.  This  kind  of  defect  in  the 
sense  of  color  leads  —  if  we  fancy  it  carried  to  its  highest 
degree,  or  in  such  a  condition  that  all  the  elements  lose  sen- 
sibility —  to  the  complete  absence  of  perception  of  light ; 
that  is  to  say,  to  blindness,  strictly  so  called.  Every  defect 
in  the  sense  of  color  must  then  proceed  either  from  a  sensi- 
oility  anomalously  reduced  to  a  complete  paralysis  of  one 
or  several  kinds  of  elements,  or  from  a  number  relatively 
diminished  in  sensibility  to  the  complete  absence  of  one  or 
several  amongst  them. 

"  The  experience  acquired  by  an  examination  of  colors  in 


ITS   DANGERS   AND   ITS   DETECTION.  37 

different  parts  of  the  visual  field  elucidates  our  theory  of 
color-blindness,  while  at  the  same  time  having  a  practical 
value.  The  following  is  the  manner  in  which  this  exami- 
nation is  conducted  :  The  eye  is  fixed  upon  an  immovable 
point;  a  colored  object — for  example,  a  colored  paper  one 
or  two  centimetres  square  —  is  slowly  passed  from  the  side 
of  the  visual  field  toward  the  fixed  point.  This  experiment 
is  performed  still  better  by  means  of  a  special  instrument, 
Forster's  perimeter.  We  then  find  that  the  colored  surface 
of  any  color  whatsoever  appears  completely  colorless  at  the 
extreme  periphery  of  the  visual  field.  Surfaces  of  different 
colors  exhibit  only  variations  in  intensity  of  light,  not  in 
color.  The  ground  on  which  the  surface  appears  plays  here 
an  important  part,  since,  every  time  our  visual  sense  per- 
ceives the  light  and  color  of  an  object,  it  partly  depends 
upon  the  comparison  with  that  which  surrounds  it.  Thus 
a  colored  surface  seems  to  us,  in  this  part  of  the  visual  field, 
black  or  gray  on  a  light  ground,  and  gray  or  white  on  a 
dark.  If,  while  following  the  same  direction,  the  colored 
object  is  carried  within  the  region  which  surrounds  the  rest 
of  the  visual  field,  like  a  belt  of  greater  or  less  width,  we 
begin  to  see  the  colored  object,  but  not  always  in  its  natural 
color.  Two  colors  alone — yellow  and  blue — retain  their 
natural  colors.  All  the  others  have  the  appearance  of  one  of 
these  colors  consequently,  —  yellow  or  blue.  It  is  only  after 
the  colored  object  is  carried  a  little  farther  toward  the  fixed 
object  that  it  is  seen  in  its  natural  color.  Consequently  we 
normally  see  colors  only  in  the  middle  of  our  visual  field, 
within  a  compass  extending  in  a  more  or  less  eccentric  man- 
ner in  every  direction  from  the  fixed  point.  Outside  of  the 
central  field  extends  a  belt  which  surrounds  it  on  all  sides, 
and  in  which  our  whole  system  of  colors  is  classed  under 
'•.wo  heads, — exactly  as  in  the  case  of  the  red-blind.  We 
have  here,  as  in  the  last  case,  but  two  colors,  —  yellow  and 
blue.  In  other  words,  we  are  completely  red-blind  in  this 
intermediary  zone  :  beyond  this  there  is  a  peripheral  belt, 
in  which  we  are  totally  color-blind.  These  are  matters  \m- 
questionably  of  great  theoretic  value ;  but  it  must  be  acknowl- 
edged they  are  also  of  great  practical  importance.  Although 
we  have  adopted  the  Young-Helmholtz  theory,  we  must 
admit  that  the  different  kinds  of  perceptive  elements  of  col- 


y»  COLOR-BLINDNESS  : 

ors  have  a  different  local  division  upon  the  retina ;  and  this 
is  why  we  may  speak  of  the  topography  of  the  chromatic 
sense.  The  fact  is  explained  in  this  way  :  in  the  retina  of 
the  normal  eye  there  are  simultaneously  three  kinds  of  ele- 
ments in  the  central  part,  corresponding  to  the  central 
region  of  the  visual  field.  Toward  the  periphery,  beginning 
at  the  central  fossa,  the  elements  become  more  and  more 
rare,  but  in  unequal  proportions ;  so  that  the  perceptive 
organs  of  red  cease  first,  and  this  at  a  limit  corresponding  to 
that  of  the  central  region.  In  a  belt  which  answers  to  the 
intermediate  zone,  or  the  belt  of  the  red-blind,  there  re- 
mains in  consequence  but  the  perceptive  elements  of  green 
and  violet.  At  the  limit  near  the  periphery  of  the  retina,  cor- 
responding to  that  of  the  peripheral  zone  of  the  visual  field, 
or  region  of  absolute  color-blindness,  the  perceptive  ele- 
ments of  green  cease  also;  so  that  there  only  remains  in  this 
last  zone  the  perceptive  elements  of  violet.  "We  have  been 
especially  led  to  this  last  conclusion  by  the  examination  of 
two  cases  of  color-blindness,  where  the  visual  field  was  so 
abnormally  small  that  the  peripheral  zone  seemed  to  be 
effaced,  and  where  we,  besides,  recognized  the  characteristic 
features  of  violet-blindness.  This  experiment,  which  per- 
fectly harmonized  with  the  theory,  showed  us  the  relation 
of  complete  red-blindness  to  the  normal  chromatic  sense. 
Red-blindness  is  distinguished  from  the  normal  sight  in  this, 
that  the  normal  central  field  is  wanting,  but  is  replaced  by  a 
mean  corresponding  at  the  same  time  to  the  central  field  and 
to  the  intermediary  zone  of  the  normal  sight.  We  have  also 
succeeded,  owing  to  the  peripheral  investigation  of  the  col- 
ored visual  field,  in  verifying  in  a  great  number  of  cases 
the  continuous  series  of  forms  of  transition,  which  we  have 
classified  as  one  kind  under  the  head  of  incomplete  color- 
blindness,  or,  in  the  instance  especially  occupying  us  here, 
incomplete  red-blindness.  In  the  same  way  the  other  kinds 
of  color-blindness  may  also,  as  regards  the  visual  field,  be 
classified  according  to  the  theory.  The  visual  field  of  the 
green-blind  is  distinguished  from  that  of  the  normal  observer 
in  this,  that  it  has  a  peripheral  field  corresponding  in  exten- 
sion both  to  the  intermediary  and  peripheral  zones  of  the 
normal  observer.  The  visual  field  of  the  violet-blind  is  dis- 
tinguished on  the  other  hand  in  this,  that  it  is  completely 


ITS   DANGERS   AND   ITS   DETECTION.  39 

deficient  in  the  normal  peripheral  zone.  These  two  kinds 
of  incomplete  color-blindness  are  characterized  by  a  central 
field  diminished  at  every  degree.  With  regard  to  the  visual 
field,  we  may  therefore  lay  down  this  rule,  that  it  has  as 
many  distinct  zones,  with  reference  to  the  perception  of 
colors,  as  the  chromatic  sense  has  fundamental  colors  or 
different  kinds  of  perceptive  elements,  and  that  the  differ- 
ent degrees  of  incomplete  color-blindness  are  in  the  inverse 
ratio  to  the  dimension  of  the  visual  field.  If  the  central 
field  is  limited  to  a  circle  of  ten  degrees  from  the  fixed 
point,  all  the  respective  characteristics  of  color-blindness 
are  usually  found  in  it,  sometimes  within  even  a  narrower 
.-ange.  A  feeble  sense  of  color  manifests  itself  in  a  much 
wider  central  field.  All  the  anomalies  that  can  be  discovered 
in  an  examination  of  the  visual  field  might,  in  consequence 
of  the  method  employed,  be  explained  by  a  diminution  of 
excitability  as  well  as  of  the  number  of  the  elements.  The 
intermediary  zone  of  the  normal  visual  field  or  belt  of  red- 
blindness  has  an  especial  interest,  as  it  furnishes  us  with 
the  opportunity  of  seeing  with  our  own  eyes  as  the  red- 
blind  sees,  and  consequently  of  exactly  comprehending  his 
abnormal  perception. 

"According  to  the  theory,  we  see  only  yellow  and  blue  in 
this  belt,  and  in  consequence  we  admit  that  the  red-blind 
not  only  call  yellow  and  blue  their  principal  colors,  but 
moreover  see  them  exactly  as  the  normal  observer  does. 
This  hypothesis  cannot  assuredly  be  proved ;  but  this  is  not 
necessary,  as  the  explanation  Helmholtz  has  given  of  the 
designation  of  one  of  the  principal  colors  of  the  red-blind  is 
perfectly  satisfactory.  This  circumstance,  however,  has 
given  rise,  amongst  others,  to  a  doubt  about  the  Young- 
Helmholtz  theory,  and  to  another  theory  admitting  four 
principal  colors  to  the  normal  sense  of  colors,  yellow  being 
classed  amongst  them.  But  this  is  useless.  It  must  not 
be  forgotten  that  colorless  light  and  colored  light  are  sub- 
jective perceptions,  and  that  comparison  here  performs  an 
important  part.  This  fact  is  sufficiently  proved  by  the  phe- 
nomena of  contrasts,  accidental  colors,  &c.  White  is  not  a 
color :  it  is  merely  a  general,  neutral  light,  and  is  therefore 
produced  when  one  kind  of  element  is  not  more  excited  than 
another,  or  when  all  the  elements  are  equally  excited. 


40  COLOR-BLINDNESS  : 

"  But,  as  the  theory  obliges  us  to  admit  that  the  excita- 
tion of  the  perceptive  elements  of  green  and  violet  may,  in 
certain  cases,  as  in  the  instance  of  the  red-blind,  supply  the 
perception  of  white,  and  not  bluish  green ;  and  that,  in  cer- 
tain cases,  as  in  that  of  the  green-blind,  the  excitation  of 
the  perceptive  elements  of  red  and  violet  does  not  give  pur- 
ple, but  white,  —  it  is  in  no  wise  contrary  to  the  theory  to 
admit  that  the  excitation  of  the  organ  perceiving  green 
gives  the  perception  of  yellow  in  cases  where  all  that  re- 
mains, moreover,  of  the  system  of  colors  is  the  comple- 
mentary color  of  yellow ;  that  is  to  say,  blue.  The  excita- 
tion of  the  perceptive  organ  of  green  gives  the  perception  of 
green  only  on  the  retina,  or  on  a  point  of  the  retina  which 
also  contains  the  organ  perceiving  red.  But  this  is  not  the 
place  for  further  developments  of  this  theory. 


"2.  —  Classification  of  the  Different  Kinds  of 
Color-Blindness. 

"  In  the  preceding  we  have  indicated,  in  conformity  with 
the  theory,  the  different  forms  of  a  defective  sense  of  colors, 
to  which,  we  think,  should  be  applied  the  name  of  color- 
blindness, and  which,  owing  to  their  nature,  theoretically 
must  be  considered  as  of  different  kinds.  This  division 
will  be  sanctioned,  if  we  consider  the  relations  in  which  it 
stands  to  the  method  pursued  for  discovering  them,  and 
which  is  based  on  the  Young-Helmholtz  theory.  It  is  this 
we  are  about  to  explain. 

"  We  classify  the  different  kinds  of  color-blindness  under 
especial  heads,  to  be  able  the  better  to  grasp  the  whole. 
We  might,  indeed,  divide  this  blindness  into  congenital  and 
acquired ;  but  as  such  a  division  has  reference  alone  to  the 
mode  of  origin,  and  not  to  the  nature  of  this  blindness,  and 
affects  in  no  wise  the  manner  of  its  discovery,  it  has  no 
practical  importance  in  the  case  now  occupying  our  atten- 
tion. Besides,  our  division  relates,  as  does  our  entire 
memoir  on  this  subject,  essentially  to  congenital  color- 
blindness.    The  division  is  as  follows  :  — 

"I.  Total  color-blindness,  in  which  the  faculty  of  perceiv- 
ing colors  is  absolutely  wanting,  and  where  the  visual  sense 
consequently  can  only  perceive  the  difference  between  dark- 


ITS   DANGERS   AXD    ITS   DETECTION.  11 

ness  and  light,  as  well  as  the  different  degrees  of  intensity 
of  light. 

"  n.  Partial  color-blindness,  in  which  the  faculty  of  cer- 
tain perceptions  of  color,  but  not  of  all,  is  wanting.  It  is 
sub-divided  into,  — 

"  1.  Complete  color-blindness,  in  which  one  of  the  three 
fundamental  sensations,  one  of  the  three  perceptive  organs 
of  color  in  the  retina,  is  wanting,  and  in  which,  conse- 
quently, the  colored  visual  field  has  but  two  ranges.  This 
group  includes  three  kinds ;  namely,  — 

"  (a)  Red-blindness. 

"  (5)   Green-blindness. 

"  (0  Violet-blindness. 

"2.  Incomplete  color-blindness,  where  one  of  the  three 
kinds  of  elements,  or  perhaps  all,  are  inferior  in  excitability 
or  in  numbers  to  those  of  the  normal  chromatic  sense.  In- 
complete color-blindness  exhibits,  like  the  normal  sense, 
three  zones  in  the  visual  field,  but  is  distinguished  from  it 
by  an  unusually  small  central  field.  This  group  includes 
the  whole  of  a  series  of  different  forms  and  degrees,  a  part 
of  which  —  the  superior  degrees,  which  might  be  called 
incomplete  red-blindness  and  incomplete  green-hlindness  (and 
incomplete  violet-blindness')  —  constitutes  the  transitions  to 
the  corresponding  kinds  of  complete  color-blindness ;  and 
another  2:'art  of  which  —  the  inferior  degrees,  which  we  call 
a  feeble  chromatic  sense  —  constitutes  the  transition  to  the 
normal  sense  of  colors. 

"  We  will  show  farther  on  that  this  classification,  based 
entirely  upon  the  Young-Helmholtz  theory,  is  quite  practi- 
cal, and  conformable  to  experience.  We  know  no  classifi- 
cation, which,  though  distinguishing  accurately  between  the 
different  essential  forms  of  a  defective  sense  of  colors,  draws 
a  surer,  more  decided,  and  more  practical  limit  between  the 
defective  sense  of  -colors  and  the  normal  sense. 


42  COLOR-BLINDNESS 


CHAPTER  V. 

PRECISE    CONDITION    OF   THE   VISION    OF   THE 
COLOR-BLIND. 

It  will  be  now  asked,  What  do  the  color-blind 
see  ?  Does  red  look  green  to  them,  or  green  red, 
or  yellow  blue,  &c.  ?  The  fact  so  long  ago  noticed 
that  they  could  not  distinguish  their  faulty  color 
from  gray,  —  a  mixture  of  black  and  white, — 
and  the  more  color-blind  they  were  the  darker  the 
gray  which  would  match  their  faulty  color,  ought, 
perhaps,  to  have  had  more  attention  paid  to  it. 
Through  this  we  can,  perhaps,  get  a  better  idea 
of  the  color-blind's  vision.  And  we  may  formu- 
late their  vision  thus  :  All  colors  containing  their 
defective  one  will  be  grayish,  and  this  in  proportion 
to  their  individual  amount  of  defect. 

But  let  us  have  the  testimony  of  the  color- 
blind themselves.  Mr.  Pole,  a  red-blind,  has 
tested  himself,  and  shown  why  his  results  should 
be  accepted.  He  thoroughly  understands  his  own 
condition,  although  he  does  not  seem  to  quite  ap- 
preciate the  existence  of  varying  degrees  of  color- 
blindness, so  perfectly  shown,  for  instance,  by 
Bonders  in  his  examination  of  the  railroad  em- 


ITS  DANGERS   AND   ITS  DETECTION.  43 

ployes  in  Holland  :  moreover,  yiolet-yellow-blind- 
ness  has  no  place  for  liim,  which  is,  perhaps, 
natural. 

In  a  criticism  of  Mr.  Gladstone's  Homeric 
vision,  recently  given  in  "Nature,"  Mr.  Pole 
briefly  sketches  his  former  extended  report  of 
his  case,  and  Sir  John  Herschel's  notice  of  the 
same.  As  to  how  he  sees,  which  interests  us,  he 
says,  — 

"  In  the  first  place,  we  (the  color-blind)  see  white  and 
black,  and  their  intermediate  or  compound  gray  (provided 
they  are  free  from  alloy  with  other  colors),  precisely  as 
others  do. 

"Secondly,  there  are  two  colors  properly  so  called, — 
namely,  yellow  and  blue, — which  also,  if  unalloyed,  we  see, 
as  far  as  can  be  ascertained,  in  the  normal  manner.  But 
these  two  are  the  onbj  colors  of  which  we  have  any  sensa- 
tion ;  and  hence  the  defect  has  been  given  by  Sir  John 
Herschel  the  scientific  name  of  dichromic  vision. 

"But  now  comes  the  difficulty  of  the  explanation.  It 
may  naturally  be  asked.  Do  we  see  objects  of  other  colors, 
such  as  roses,  grass,  violets,  oranges,  and  so  on  ?  And,  if  we 
do  see  them,  what  do  they  look  like  ?  The  answer  is,  that 
we  do  see  all  such  things,  but  that  they  do  not  give  us  the 
color-sensations  correctly  belonging  to  them  :  their  colors 
appear  to  us  varieties  of  the  other  color-sensations  which 
we  are  able  to  receive.  This  will  be  best  explained  by 
examples.  Take  first  the  color  red.  A  soldier's  coat 
(British),  or  a  stick  of  red  sealing-wax,  conveys  to  me  a 
very  positive  sensation  of  color,  by  which  I  am  perfectly 
able  to  identify,  in  a  great  number  of  instances,  bodies  of 
this  hue.  If,  therefore,  the  investigation  of  my  experience 
ended  here,  there  would  be  no  reason  to  consider  me  blind 
to  red,  or  as  having  any  grave  defect  in  my  vision  regarding 
it.  But,  when  I  examine  more  closely  what  I  really  do  see, 
I  am  obliged  to  come  to  the  conclusion  that  the  sensation  I 
perceive  is  not  one  that  I  can  identify  separately,  but  is 
simply  a  modification  of  one  of  my  other  sensations ;  namely, 
yellow.     It  is,  in  fact,  a  yellow,  shaded  with  black  or  gray 


44  COLOE-BLINDNESS  : 

—  a  darkened  yellow,  or  what  I  may  call  yellow  brown.  I 
find  that  all  the  most  common  hues  of  red  correspond  with 
this  description ;  and,  in  pro]Dortion  as  they  are  more  scarlet 
or  more  tending  towards  orange,  the  yellow  I  see  is  more 
vivid.  The  explanation,  I  suppose,  is,  that  none  of  such 
reds  are  pure,  —  they  are  combinations  of  red  with  yellow; 
so  that  I  see  the  yellow  element  of  the  combination,  while 
the  true  red  element  of  the  combination  is  invisible  to  me 
as  a  color,  and  acts  only  as  a  darkening  shade. 

"  I  obtain  a  further  proof  of  this  by  the  change  of  sensa- 
tion when  the  hue  of  red  is  altered.  I  find,  that,  as  the  color 
approaches  crimson,  the  yellow  element  becomes  fainter, 
and  the  darkening  shade  more  powerful,  until  very  soon  the 
yellow  disappears,  and  nothing  but  a  gray  or  colorless  hue 
is  presented  to  my  eye,  although  the  color  is  still  a  positive 
and  powerful  red  to  the  normal-eyed ;  so  that  there  is  a 
hue  of  red,  which,  as  a  color,  is  absolutely  invisible  to  the 
color-blind. 

"  If  I  go  on  beyond  this  point,  and  take  reds  that  pass 
from  crimson  towards  the  hue  called  lake,  I  see  my  other 
color  come  in,  —  a  faint  blue,  —  which  increases  till  violet  is 
reached,  when  it  becomes  more  decided.  Violet  is  under- 
stood, I  believe,  to  be  a  compound  of  blue  with  red ;  and, 
accordingly,  the  red  element  being  invisible  to  the  color- 
blind, violet  hues  generally  appear  to  them  only  as  darkened 
blue.  There  are,  however,  examples  where,  from  the  red 
being  very  strong,  the  blue  appears  to  lose  its  effect ;  and 
the  impression  given  is  colorless,  black,  or  gray.  They 
correspond,  in  fact,  with  the  neutral  red  before  described, 
although  still  called  violet  or  purple  by  the  normal-eyed. 
This  latter  effect  is  much  enhanced  under  the  artificial  light 
of  gas  or  candles. 

"  A  similar  observation  will  apply  to  orange,  —  a  com- 
bination of  red  and  yellow,  —  in  which  the  yellow  only  is 
perceived, 

"  The  appearance  of  green  to  the  color-blind  corresponds 
exactly  to  that  of  red.  Green,  in  its  true  aspect,  is  invisible 
to  them;  and,  consequently,  when  neutral,  —  i.e.,  unmixed 
with  any  other  color,  — it  presents  to  their  eyes  the  appearance 
of  gray.  When,  however,  it  is  mixed  with  yellow  (and  most 
of  the  greens  in  nature  are  yellow  greens),  they  see  the 


ITS   DANGERS   AND   ITS   DETECTION.  45 

yellow  only,  but  diluted  or  darkened  by  the  invisible  green 
element;  and  in  less  frequent  cases,  Tvhere  the  green  is 
mixed  with  blue,  they  see  the  blue  element  only  in  like 
manner. 

"It  is  therefore  easily  understood  how  so  simple  a  defect 
of  vision  gives  rise  to  so  complex  a  series  of  symptoms  as 
those  already  described.  Take  first  the  color  red.  If  it  is 
a  scarlet  variety,  as  the  majority  of  reds  are,  presenting  the 
appearance  of  yellow  to  the  color-blind,  they  may  naturally 
confound  it  with  the  latter  color,  as  well  as  with  orange, 
with  yellow  green,  and  with  brown,  —  all  which  cause  to 
them  the  same  sensation.  If,  on  the  other  hand,  the  red 
contains  a  predominance  of  blue,  it  may  be  confounded, 
on  the  same  principle,  with  blue  or  violet.  If  it  is  a 
neutral  red,  lying  between  the  two,  it  will  be  confounded 
with  black  or  gray.  A  pale  pink,  though  very  distinctly 
colored  to  the  normal-eyed,  often  offers  so  little  color  to  the 
color-blind  as  to  be  mistaken  for  white  or  very  light  gray. 
The  same  explanation  will  apply  to  green.  Its  yellow 
varieties  may  be  compounded  with  red,  orange,  yellow, 
and  brown  ;  its  blue  varieties  with  blue  and  violet  ;  and  its 
neutral  hue  with  black  or  gray,  or,  if  pale,  with  white." 

These  statements  of  Mr.  Pole  are  so  valuable, 
and  so  in  accordance  with  the  application  of  the 
Young-Helmholtz  theory  of  color-perception  to 
color-blindness  as  we  now  are  enabled  to  analyze 
it,  that  I  can  not  refrain  from  quoting  Sir.  John 
Herschel's  remarks  in  reference  to  them.  We  see 
now  how  the  color-blind  perceive  the  colors  they 
are  blind  to ;  and  therefore  it  is  important  to  feel 
assured  that  the  red-blind  —  as,  for  instance,  Mr. 
Pole's  —  perception  of  yellow  and  blue  is  the  same 
as  our  own  or  the  normal-eyed.     Sir  John  says,  — 

"I  consider  this  paper  as  in  many  respects  an  exceed- 
ingly valuable  contribution  to  our  knowledge  of  the  curious 
subject  of  color-blindness,  —  first,  because  it  is  the  only  clear 
and  consecutive  account  of  that  affection  which  has  yet  been 
given  by  a  party  affected  in  possession  of  a  knowledge  of 


46  COLOR-BLIXDKESS : 

what  has  been  said  and  written  on  it  by  others,  and  of  the 
theories  advanced  to  account  for  it,  and  who,  from  general 
education  and  habits  of  mind,  is  in  a  position  to  discuss  his 
own  case  scientifically ;  and,  second,  for  the  reasons  the  au- 
thor himself  alleges  why  such  a  person  is  really  more  fa- 
vorably situated  for  describing  the  phenomena  of  color- 
blindness than  any  normal-eyed  person  can  possibly  be.  It 
is  obvious  that  on  the  very  same  principle  that  the  latter  con- 
siders himself  entitled  to  refer  all  his  perceptions  of  color 
to  three  primary  or  elementary  sensations,  —  whether  these 
be  red,  blue,  and  yellow,  as  Mayer  (followed  in  this  respect 
by  the  generality  of  those  who  have  written  on  colors)  has 
done,  or  red,  green,  and  violet,  as  suggested  by  Dr.  Young, 
reasoning  on  Wollaston's  account  of  the  appearance  of  the 
spectrum  to  his  eyes,  —  on  the  very  same  principle  is  a  per- 
son in  Mr.  Pole's  condition,  or  one  of  any  other  description 
of  abnormal  color-vision,  quite  equally  entitled  to  be  heard 
when  he  declares  that  he  refers  his  sensations  of  color  to  two 
primary  elements,  whose  combination  in  various  proportions 
he  recognizes,  or  thinks  he  recognizes,  in  all  hues  presented 
to  him,  and  which,  if  he  pleases  to  call  yellow  and  blue,  no 
one  can  gainsay  him;  though,  whether  these  terms  express 
to  him  the  same  sensation  they  suggest  to  us,  or  whether  his 
sensation  of  light  with  absence  of  color  corresponds  to  our 
white,  is  a  question  which  must  forever  remain  open 
(although  I  think  it  probable  that  such  is  really  the  case). 
All  we  are  entitled  to  require  on  receiving  such  testimony  is, 
that  the  party  giving  it  should  have  undergone  that  sort  of 
education  of  the  sight  and  judgment,  esjDecially  with  reference 
to  the  primitive  decomposition  of  natural  and  artificial  col- 
ors, for  want  of  which  the  generality  of  persons  whose  vision 
is  unimpeachably  normal  appear  to  entertain  very  confused 
notions,  and  are  quite  incai)able  of  discussing  the  subject  of 
color  in  a  manner  satisfactory  to  the  photologist. 

"  That  Mr.  Pole's  vision  is  rfzchromic,  however,  there  can 
be  no  doubt.  If  I  could  ever  have  entertained  any  as  to  the 
correctness  of  the  views  I  have  embodied  of  the  subject  in 
that  epithet,  after  reading  ail  I  have  been  able  to  meet  with 
respecting  it,  this  paper  would  have  dispelled  it.  That  he 
sees  blue  as  we  do,  there  is  no  ground  for  doubting ;  and  I 
think  it  extremely  likely  that  his  sensation  of  whiteness  is 


ITS   DAJTGERS   AND  ITS   DETECTION.  47 

the  same  as  ours.  Whether  his  sensation  of  yellow  corre- 
sponds to  ours  of  yellow  or  of  green,  it  is  impossible  to 
decide,  though  the  former  seems  to  be  most  likely." 

We  thus  see  that  the  color-sense  of  the  color- 
blind may  be  described  as  follows :  The  red-blind 
sees  all  objects  of  this  color  of  a  darker  hue  than 
they  are.  The  same  of  the  green-blind  as  to 
green.  Both  confound  these  colors  with  each 
other  and  gray.  A  mixture  of  white  and  black  in 
proper  proportions,  to  represent  the  luminosity  of 
any  shade  of  red  or  green,  will  give  the  color-blind 
the  same  sensation  as  that  shade.  The  violet-yel- 
low-blind will  do  the  same  in  reference  to  all  colors 
containing  either  of  these  two.  Violet-blindness  is 
so  extremely  rare,  and  not  causing  danger  on  land 
or  sea,  we  may  omit  special  discussion  of  it. 
Great  misunderstanding  of  the  color-blind's  sensa- 
tion has  arisen  from  the  natural  lack  of  knowledge 
and  appreciation  of  composite  colors.  Purple,  or  a 
combination  of  red  and  violet,  or  blue,  is  rarely 
otherwise  spoken  of  than  red  in  popular  language, 
except  when  the  commercial  name  "  magenta  "  is 
used.  The  blue  or  violet  in  it  the  normal-eyed  do 
not  think  of,  and  none  would  class  it  with  blue. 
The  color-blind,  however,  do  not  see  the  red  in  it 
other  than  gray ;  but,  as  their  vision  is  perfect  for 
violet,  they  see  this  in  the  purple,  and  so  class  it 
with  blue.  Hence  the  general  idea  that  the  color- 
blind confound  red  with  blue,  the  sky  and  a  rose. 
Pure  red  they  never  confound  with  blue. 


48  COLOE-BLINDNESS 


CHAPTER  yi. 

COLOE-BLINDNESS   FROM  DISEASE  OR  INJURY. 

/  Color-blindness  is  a  congenital  defect,"  and,  as 
will  be  later  shown,  incurable.  It  is  not  connected 
with  any  special  color  of  the  eyes,  or  the  humors 
within  the  eyeball.  The  color  of  the  eye  depends 
on  the  more  or  less  pigment  in  the  iris.  The  back 
of  this  little  screen  is  covered  with  black  pigment, 
preventing  light  passing  through  it,  so  that  its 
color  can  have  no  effect.  The  ocular  humors  of 
a  color-blind  person  have  been  found  exactly  the 
same  as  the  normal-eyed.  Whether  color-blind- 
ness is  caused  by  some  defect  in  the  recijnent  organ, 
the  retina,  or  the  perceptive  organ,  the  brain,  or 
both,  is  not  yet  decided /and  I  need  not  discuss 
the  question  here. 

^It  is  of  more  importance  to  know  and  remember 
that  a  similar  condition  as  to  blindness  to  color  is 
caused  by  certain  diseases  of  the  eye  or  brain. 
Ophthalmic  surgeons  have  long  known  that  a  loss 
of  chromatic  sense  was  associated  with  a  peculiar 
form  of  atrophy  of  the  optic  nerve,  which  is 
hereditary.  Certain  constitutional  diseases,  also, 
cause  color-blindness.     In  some  affections  of  the 


ITS   DANGERS   AND   ITS   DETECTION.  49 

eye  alone,  portions  of  the  retina  become  color- 
blind. As  with  simple  congenital  color-blindness, 
the  power  of  form-perception,  in  chromatic  loss 
from  disease,  may  be  retained. 

Tobacco  and  alcohol,  either  alone  or  together, 
may  finally  cause  color-blindness.  The  warnings 
of  ophthalmic  surgeons  have  been  too  little  heeded 
on  this  point.  The  loss  of  color-perception  is 
often  overlooked,  as  the  loss  of  form-perception 
most  troubles  the  person  affected.  Excessive 
smokers  and  drinkers  amongst  railroad  employes 
and  sailors  may  become  color-blind  when  their  eye- 
sight is  still  good  enough  for  them  to  retain  their 
positions,  in  which  perfect  color-perception  is  also 
needed. 

Color-blindness  is  caused  also  by  accidents,  and 
especially  by  those  accompanied  with  excessive  jar 
and  shock,  as  on  railroads.  There  are  many  well- 
authenticated  cases  on  record  where  normal  color- 
perception  was  known  to  exist  before  the  accident. 
Professor  Wilson  reports  a  physician  who  was 
thrown  from  his  horse,  and  suffered  great  cerebral 
disturbance.  On  recovering  sufficiently  to  notice 
distinctly  objects  around  him,  he  found  his  percep- 
tion of  colors  weakened  and  perverted,  and  has 
since  continued  so.  Flowers  have  lost  more  than 
half  their  beauty  for  him  ;  and  he  still  recalls  the 
shock  which  he  experienced  on  first  entering  his 
garden,  after  his  recovery,  at  finding  that  a  favorite 
damask  rose  had  become  in  all  its  parts, — petals, 
leaves,  and  stem,  —  of  one  uniform  dull  color,  and 
that  variegated  flowers,  such  as  carnations,  had 
lost  their  characteristic  tints. 


50  COLOR-BLINDNESS  : 

Dr.  Favre  reports  several  interesting  cases  of 
temporary  color-blindness  from  injury,  and  says,  — 

"The  majority  of  cases  of  traumatic  color-blindness  are 
very  analagous  to  congenital  natural  chromatic  deficiency. 
Railroad  employes  and  sailors  are  certainly  amongst  those 
who  are  most  exposed  to  wounds  and  contusions.  The  large 
majority  of  such  are  habitually  or  occasionally  charged  with 
the  observation  or  transmission  of  orders  given  by  colored 
signals.  Railroad  officials  and  naval  officers  ought  therefore 
to  have  their  attention  called  to  the  circumstances  which 
may  at  a  given  moment  and  for  a  certain  time  deprive  an 
engineer,  a  stoker,  a  conductor,  a  pointsman,  a  station-mas- 
ter, a  guard,  a  sailor  at  the  helm,  a  lighthouse-keeper,  a  sig- 
nal-man, or  a  coast-guardsman,  of  their  correct  j  udgment  of 
colors." 

In  illustration  of  color-blindness  from  disease,  I 
will  mention  Dr.  Hay's  case  :  A  young  woman  aged 
twenty  had  cerebral  trouble,  and,  with  some  loss  of 
sight,  considerable  loss  of  color-perception.  When 
asked  whether  she  could  see  the  figure  on  her  dress, 
which  was  a  calico  one  with  red  spots,  she  re^^lied, 
"  Yes,  I  see  the  hrown  s^jots.^''  It  was  ascertained 
she  could  distinguish  forms,  even  of  small  size, 
with  accuracy ;  but  her  perception  of  colors  was 
exceedingly  imperfect.  Repeated  and  careful  in- 
vestigations during  this  and  on  several  subsequent 
occasions  showed  that  the  only  colors  she  knew 
with  certainty  were  yellotv  and  blue.  Nearly  all 
other  colors  she  termed  brown,  or  hesitated  to 
name,  designating,  however,  their  shades  or  inten- 
sity of  color  accurately.  Thus  a  deep  red  she 
called  a  dark  brown  ;  a  bright  green,  a  light  brown  ; 
and  a  very  pale  pink,  a  very  light  shade  of  brown. 
She  was  not  congenitally  color-blind,  and,  after 
some  months  of  treatment,  recovered  her  form  and 
color  perception  perfectly.  She  resembled  a  red- 
blind  person  whilst  suffering  from  her  disease. 


ITS   DANGERS   AND   ITS   DETECTION.  51 

Tynclall  reports  a  case  of  Mr.  White  Cooper's, 
which,  as  it  contains  a  word  of  warning",  and  is  be- 
sides very  interesting,  I  will  give  at  length :  — 

"  The  sufferer  was  a  sea-captain,  and  ten  or  twelve  years 
ago  was  accustomed,  when  time  lay  heavy  on  his  hands,  to 
occupy  it  by  working  at  embroidery.  Being  engaged  one 
afternoon  upon  a  piece  of  work  of  this  description,  and  anx- 
ious to  finish  a  flower  (a  red  one,  he  believes),  he  prolonged 
his  labors  until  twilight  fell,  and  he  found  it  difficult  to  select 
the  suitable  colors.  To  obtain  more  light  he  went  into  the 
companion,  or  entrance  to  the  cabin,  and  there  continued  his 
needle-work.  While  thus  taxing  his  eyes,  his  power  of  dis- 
tinguishing the  colors  suddenly  vanished.  He  went  upon 
deck,  hoping  an  increase  of  light  would  restore  his  vision. 
In  vain.  From  that  time  to  the  present  he  has  remained 
color-blind.  Berlin  worsted,  with  which  he  had  been  ac- 
customed to  work,  he  at  once  and  correctly  pronounced  to  be 
bins'.  He  had  a  keen  appreciation  for  this  color,  and  never 
made  a  mistake  regarding  it.  Two  bundles  of  worsted 
—  one  a  light  green,  and  the  other  a  vivid  scarlet  —  were 
next  placed  before  him.  He  pronounced  them  to  be  both  of 
the  same  color.  A  difference  of  shade  was  perceptible  ;  but 
both  to  him  were  drab.  A  green  glass  and  a  red  glass  were 
placed  side  by  side  between  him  and  the  window  :  he  could 
discern  .  no  difference  between  the  colors.  A  very  dark 
green  he  pronounced  to  be  black ;  the  purple  covering  of  the 
chairs  was  also  black;  a  deep  red  rose  on  the  wall  of  the 
room  was  a  mere  blotch  of  black  ;  fruits,  partly  of  a  bright 
red  and  partly  of  a  deep  green,  were  pronounced  to  be  of 
the  same  uniform  color.  A  cedar  pencil  and  a  stick  of  seal- 
ing-wax placed  side  by  side  were  nearly  alike.  The  former 
was  rather  brown ;  the  latter,  a  drab.  Electric  light  through 
a  green  glass,  allowed  to  fall  on  a  screen,  gave  him  no 
color ;  but  only  that  portion  of  the  screen  Avas  a  little  less  in- 
tensely illuminated. 

"  Capt.  C.  was  assured,  that,  previous  to  the  circum- 
stances related,  he  was  a  good  judge  of  colors;  so  that,  pro- 
nouncing on  any  color,  he  has  an  aid  from  memory  not 
usually  possessed  by  the  color-blind.  Indeed,  he  had  an 
opportunity  of  reviving  his  impression  of  red.     A  glass  of 


52  COLOR-BLINDNESS  : 

this  color  was  placed  before  his  ej^es  while  he  stood  close  to 
the  electric  lamp.  On  establishing  the  light,  he  at  once  ex- 
claimed, 'That  is  red!  '  He  appeared  greatly  delighted  to 
renew  his  acquaintance  with  this  color,  and  he  declared  he 
had  not  seen  it  for  several  years.  The  glass  was  then  held 
near  the  light,  while  he  went  to  a  distance :  but  in  this  case 
no  color  was  manifest;  neither  was  any  color  seen  when  a 
gas-lamp  was  regarded  through  the  same  glass.  The  in- 
tense action  due  to  proximity  to  the  electric  light  appeared 
necessary  to  produce  the  effect.  Capt.  C.'s  interest  in 
this  experiment  was  increased  by  the  fact  that  the  Portland 
light,  which  he  has  occasion  to  observe,  has  been  recently 
changed  from  green  to  red  ;  but  he  has  not  been  able  to 
recognize  this  change.  The  fare  in  the  fore-cabin  of  a 
vessel  of  his  own,  which  he  now  commands,  happens  to  be 
sixpence ;  and  he  is  often  reminded  by  the  passengers  that 
he  has  not  returned  their  change.  The  reason  is,  that  he 
confounds  a  sixpence  with  a  half-sovereign,  both  being  to 
him  of  the  same  color.  A  short  time  ago  he  gave  a  sover- 
eign to  a  waterman,  believing  it  to  be  a  shilling." 

Mr.  Haynes  Walton  says,  — 

"  A  few  years  ago  I  was  investigating  color-appreciation, 
and  the  first  instance  of  the  acquired  defect  that  came  to 
my  knowledge  was  in  the  person  of  an  engine-driver.  This 
man  confessed,  after  an  accident  through  his  not  distin- 
guishing the  red  signal,  that  he  had  gradually  lost  his  color- 
power,  which  had  been  perfect ;  and  so  sensible  was  he  of 
his  loss  and  its  disadvantages,  that,  before  the  accident,  he 
had  determined  to  give  up  the  situation.  The  manager  of 
the  company,  who  told  me  the  circumstance,  assured  me 
that  this  driver  had  been  carefully  examined  but  a  few  years 
back,  and  passed  as  possessing  perfect  sight.  Does  not  this 
show  that  those  who  are  to  be  trusted  with  color-signals 
should  be  periodically  examined?  " 

We  have  thus  seen  that  there  is  a  condition 
wholly  resembling  congenital  color-blindness, 
caused  by  disease  or  accident,  and  that  it  may  be 
recovered  from  when  the  results  of  disease  or  acci- 
dent pass  away.     This   must  be  remembered,  as 


ITS   DANGERS   AND   ITS   DETECTION.  53 

color-blindness,  when  congenital,  is  incurable.  To 
the  ophthalmic  surgeon  color-blindness  is  a  recog- 
nized symptom  of  certain  affections.  This  is  a 
question  discussed  in  ophthalmic  literature,  and 
out  of  place  here  further  than  I  have  introduced 
it.  The  abuse  of  alcohol  and  tobacco  is  too  com- 
mon not  to  render  possible  color-blindness  from 
this  cause  among  railroad  employes  and  sailors,  — 
a  point  at  least  to  be  remembered. 


64  COLOR-BLINDNESS 


CHAPTER  YII. 

COLOE-BLINDNESS   HEREDITAEY. 

Like  all  other  congenital  defects,  color-blind- 
ness is  hereditary,  which  explains  the  large  ratio 
of  color-blindness  individual  observers  have  found 
when  happening  to  include  one  or  more  color- 
blind families  in  their  statistics.  In  1845  Dr. 
Pliny  Earle  reported  the  color-blindness  of  five 
generations  of  his  family  as  follows :  — 

Of  the  first  he  knows  nothing  as  to  their  color- 
blindness. 

Second:  of  seven  brothers  and  eight  sisters, 
three  brothers  had  the  defect.  One  was  Dr. 
Earle's  grandfather. 

Third  generation,  —  children  of  the  grandfather, 
—  three  brothers  and  four  sisters :  no  one  imper- 
fect. 

Fourth  generation, — first  family  of  five  brothers 
and  four  sisters :  two  brothers  color-blind. 

Second  family  of  one  child  (girl)  :  normal  color- 
perception. 

Third  family  of  seven  brothers :  four  had  color- 
blindness. 

Fourth,  not  reported. 


ITS   DAXGEPvS  AKD   ITS   DETECTION.  55 

Fifth  family  of  three  brothers  and  seven  sisters : 
all  perfect  vision. 

Sixth  family  of  four  brothers,  five  sisters :  two 
of  each  sex  color-blind. 

Seventh  family  of  two  brothers,  three  sisters : 
the  two  brothers  color-blind. 

Eighth  family  :  no  issue. 

Ninth  family  of  two  sisters  with  normal  color- 
perception. 

Seventeeyi  of  these  people  of  the  fourth  genera- 
tion are  married,  and  have  fifty-two  children. 
Many  of  the  latter  are  very  young  (1845)  ;  and, 
as  the  defective  perception  has  hitherto  been  de- 
tected in  but  two  of  the  families.  Dr.  Earle  places 
these  alone  on  the  list  for  the  fifth  generation.  In 
one  of  these  families  of  three  brothers  and  three 
sisters,  one  of  the  brothers  has  the  defect ;  and  in 
the  other  a  male,  an  only  child,  is  similarly 
affected.  We  have  therefore,  in  these  thirty-two 
males,  eighteen  color-blind.  Of  the  twenty-nine 
females,  two  are  color-blind. 

The  overleaping  of  one  generation  by  the  hered- 
itary peculiarity  of  vision  is  satisfactorily  shown, 
since  it  appears  that  there  are  no  cases  in  the 
third  generation.  Furthermore,  in  the  cases  of  the 
two  males  of  the  fifth  generation,  it  will  be  per- 
ceived that  neither  parent  nor  grandparent  had 
the  defect;  so  that  there  was  an  interval  of  two 
generations  between  the  manifestations  of  that 
defect. 

Dr.  Earle  regrets  he  is  unable  to  give  me  a  fur- 
ther report  of  his  family  to  this  time  (December, 
1878). 

Such  methods  of  testing  as  are  now  only  consid- 


56  COLOR-BLIKDNESS  : 

ered  to  be  absolutely  certain  would,  perhaps,  have 
revealed  varying  degrees  of  color-blindness  in  other 
members  of  these  families. 

The  first  case  ever  reported,  the  shoemaker  Har- 
ris, had  three  brothers  color-blind  also,  whilst  two 
other  brothers  and  a  sister  were  free  from  the  de- 
fect. Dalton  had  a  brother  color-blind  like  him- 
self, another  brother  and  a  sister  normal-eyed.  In 
one  of  Dr.  Nichols's  cases  the  defect  was  derived 
from  the  maternal  grandfather,  some  of  whose 
brothers  were  also  color-blind.  In  fact,  hardly 
any  of  the  older  cases  reported  did  not  show  that 
it  was  a  family  peculiarity.     Wartman  says,  — 

"  With  respect  to  affinity,  there  are  some  color-blind  no  one 
of  whose  kindred  exhibits  this  anomaly  of  vision.  Others 
have,  so  to  speak,  inherited  it  from  their  father  or  their 
uncle,  either  paternal  or  maternal  (without,  in  the  latter 
case,  the  aunt  participating  in  it).  Lastly,  it  is  not  rare  to 
find  brothers,  several  of  whom  are  color-blind,  without  their 
being  all  necessarily  so.  The  sisters  are  almost  always 
privileged." 

We  must,  however,  remember  that,  so  long  ago 
as  when  Wartman  wrote,  this  defect  was  rather 
regarded  as  a  scientific  curiosity,  not  particularly 
affecting  practical  life.  The  blood-relatives  of  a 
color-blind  would  therefore  rarely  be  hunted  up 
and  tested. 

Cunier,  moreover,  in  1838,  rejDorts  the  case  of  a 
lady  who  was  color-blind.  Her  mother  and  two 
feisters  were  the  same.  Her  brother  was  free  from 
the  defect.  The  lady  had  six  children,  —  one  son 
not  color-blind,  and  five  daughters  affected  like  her- 
self. The  oldest  daughter  had  four  children,  two 
of  them  (girls)  color-blind.  The  second  daughter 
had  a  boy  and  a  girl,  the  latter  color-blind.     The 


ITS   DANGERS    AND    ITS    DETECTION.  57 

fourth  daughter  unmarried.  The  fifth  left  a  boy 
myopic,  but  not  color-blind.  We  thus  have  the 
remarkable  instance  of  color-blindness  appearing 
only  in  the  females  of  a  family  for  four  genera- 
tions.    Dr.  Ph.  Hochecher  says, — 

"  Many  observers  have  sho\vn  color-blindness  to  be  hered- 
itary. I  am  not  the  only  color-blind  in  my  family.  Three 
of  my  mother's  brothers  are  so,  one  of  my  cousins,  and  a 
nephew.  The  same  is  the  case  with  one  of  the  students, 
whose  case  I  report.  He  is  color-blind,  his  mother,  and  his 
mother's  brother,  as  was  also  his  brother,  now  dead." 

Heredity  was  frequently  very  marked,  known, 
and  reported  on  among  the  many  people  who  re- 
plied to  Professor  Wilson's  inquiries.  He  even 
says,  — 

"  No  fact  is  better  ascertained  than  that  color-blindness 
clings  to  certain  families,  and  is  hereditary.  "With  few  ex- 
ceptions, every  one  of  the  parties  whose  cases  I  have  spe- 
cially recorded  in  this  paper  has  near  relatives  as  color-blind 
as  himself.  It  seems,  indeed,  a  safe  estimate,  that  every 
decided  case  of  color-blindness  implies  the  existence  of 
another  case  of  equal  or  similar  severity  in  the  person  of  a 
relative  ;  so  that  the  numbers  I  have  given  as  representing 
the  proportion  of  color-blindness  in  the  community  may  be 
fairly  doubled.'' 

My  own  experience  agrees  with  Professor  Wil- 
son. Few  of  the  adult  color-blihd  whom  I  have 
tested  did  not  know  of  some  blood-relative  simi- 
larly affected.  It  has  been  found  prevalent  with 
the  Jews,  among  whom  intermarriage  and  conse- 
quent hereditary  peculiarity  is  very  frequent. 

Professor  Horner  of  Zurich  has  given  the  data 
on  which  he  based  the  law  of  transmission  of 
color-blindness,  and  they  are  of  such  value  in  ref- 
erence to  heredity,  that  I  introduce  them   here 


58  COLOR-BLINDNESS  : 

with  the  remarks  accompanymg  his  original  ar- 
ticle.    He  says,  — 

"  The  hereditariness  of  color-blindness  has  been  long 
known.  Ribot  and  Darwin  speak  of  it,  as  also  that  it  is 
more  frequent  in  men  than  women.  As  I  have  had  oppor- 
tunity of  being  familiar  with  very  accurate  pedigrees,  which 
illustrate  a  definite  law,  I  will  give  the  results  of  these  gen- 
ealogical researches. 

"  The  first  family  I  became  acquainted  with  some  years 
since.  In  the  following  Table  I.,  the  male  descendants  are 
marked  with  M,  and  the  female  with  W.  The  generations 
go  from  A  to  G.  The  letter  of  the  particular  generation 
stands  beside  the  letter  for  the  sex.  To  simplify  the  tables, 
the  unmarried  daughters,  and  the  brothers  and  sisters  whose 
descendants  could  not  be  followed,  are  omitted.  I  would, 
however,  expressly  say  that  this  omission  only  affects  the 
result  in  that  the  law  appears  more  marked,  not  that  an 
exception  to  it  is  thereby  concealed.  For  instance :  if,  in 
generation  D,  several  unmarried  normal-eyed  daughters,  in 
generation  G  some  normal-eyed  sons  not  yet  married  were 
included,  it  would  have  further  illustrated  the  law,  but  have 
rendered  the  scheme  more  difficult  to  express  in  print. 

"  From  the  youngest  generation  H,  the  tree  is  quite  cer- 
tain up  to  generation  C.  I  have  the  proofs  of  this  from 
those  who  were  living  in  the  commencement  of  the  eight- 
eenth century.  From  here  upwards  the  conclusion  as  to 
the  common  origin  is  hypothetical.  We  know  nothing  of 
the  color-blindness  of  A.  He  was  the  father  of  two  daugh- 
ters, who  have  red-blind  sons.  From  the  evident  law  among 
the  descendants,  it  is  fair  to  conclude  that  the  mothers  were 
not  color-blind,  but  the  grandfather  was.  At  any  rate,  the 
table,  even  if  we  omit  the  upper  row  as  hypothetical,  is  of 
much  interest,  and  plainly  shows,  — 

"  1st,  That  there  were  no  color-blind  girls. 

"  2d,  That  color-blind  fathers  had  normal-eyed  sons. 

"3d,  That  color-blind  sons  had  normal-eyed  mothers. 

"  4th,  That  the  seeming  exception  in  generation  F,  where 
a  color-blind  father  had  a  color-blind  son,  is  explained  as 
still  in  conformity  with  the  law  when  we  recall  that  the 
mother,  color-blind,  was  the  daughter  of  a  color-blind  father, 
and  we  have  the  descendants  of  two  color-blind. 


ITS    DANGERS   AXD   ITS   DETECTION. 


59 


TABLE    1. 

o 

UJ 

Cj 

_/^ 

2 
# 

c 

1 

,/ 

— ^ 

m 

o  ■• 

; 

> 

# 

\ 
\ 

/^o^ 

* 

i  / 

\ 

/.■'         C5    /^ 

-^^ 

c     ; 

1; 

1   • 

\ 

7    /^  "-:--, 

* 

1  . 
<  ; 

S  ': 

*    : 

el 

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EXPLANATION. 

—  The  star  (*)  denotes  those  who  were  color-blind. 

60 


COLOR-BLINDNESS  : 


ITS    DANGERS   AND   ITS   DETECTION.  61 

"  5th,  The  general  law  is,  therefore,  '.  that  sons  of  daugh- 
ters whose  father  was  color-blind  are  most  likely  to  be  the 
same,  although  not  without  exception  (vide  H)  ;  or,  color- 
blindness is  transmitted  in  the  revertible  type  from  grand- 
father to  grandchild.' 

"I  have  become  acquainted  with  another  family  tree 
which  gives,  although  to  a  lesser  extent,  the  same  type.  I 
place  it  without  comment  with  the  other,  calling  attention 
to  only  one  interesting  fact ;  namely,  a  jump  of  two  genera- 
tions. The  first  daughters  of  generation  B  bore  only  girls, 
whose  sons  followed  their  great-grandfather's  type.  In  this 
smaller  pedigree  it  is  seen  that  in  generation  C  and  D  the 
transmission  to  the  grandchildren  is  not  absolute  ;  so  that  it 
is  the  complement  of  Table  1." 

Cohn  found,  among  his  one  hundred  color-blind, 
three  times  the  father  red-blind,  fifty-six  times  the 
parents  normal-eyed ;  in  fourteen  cases  the  broth- 
ers color-blind ;  once  the  father  and  three  sons.  In 
no  case  were  all  the  children  color-blind.  A  color- 
blind father  had  seven  children,  all  normal-eyed ; 
but  the  mother's  brother,  a  cousin  of  the  mother, 
and  all  the  sons  of  this  cousin's  only  sister,  color- 
blind (none  of  the  daughters). 

Dr.  Magnus  says,  -^ 

"  The  hereditariness  of  color-blindness  has  been  known 
as  long  as  the  defect  itself.  All  who  have  seen  many  color- 
blind will  have  often  noticed  that  it  was  in  their  mother's 
family  that  other  cases  were  found.  I  have  frequently  been 
assured  that  this  or  that  cousin  on  the  mother's  side  was  also 
color-blind ;  and,  now  and  then,  that  a  more  distant  relative 
of  the  mother  had  also  color-blind  sons.  In  view  of  Homer's 
law,  this  is  readily  explainable  ;  and  this  peculiar  law  is  all 
the  more  interesting  since  we  find  that  it  is  the  same  in  ref- 
erence to  the  heredity  of  other  physiological  abnormities  or 
defects.  For  instance,  we  know  that  in  families  the  ten- 
dency to  bleeding  is  similarly  handed  down,  and  also,  as  Dr. 
Pagenstecher  has  recently  shown,  night-blindness.  It  would 
seem  as  if  this  law  of  heredity  had  a  more  general  applica- 


62  COLOE-BLESTDNESS  : 

tion.  It  would  be  most  valuable  if  family  physicians,  who 
know  and  observe  their  patients'  families  for  several  genera- 
tions, could  interest  themselves  in  carefully  elucidating  the 
extent  of  this  important  law. 

"  Naturally  this  law  does  not  exclude  the  possibility  of 
other  ways  in  which  color-blindness  may  descend.  In  some 
cases  I  have  with  certainty  found  that  a  color-blind  father 
begat  color-blind  sons.  I  remember  now  two  cases  in  which 
a  color-blind  father  had  two  color-blind  sons." 

In  a  later  publication  Dr.  Magnus  says,  — 
"  The  effect  of  heredity  is  very  marked  in  my  examina- 
tions. Of  ninety-five  color-blind,  whose  families  I  could 
inquire  about  in  reference  to  this  point,  I  found  it  in  forty- 
two.  Five  times  the  parents  were  normal-eyed,  but  the 
grandfather  color-blind,  and  in  three  of  these  cases  the 
father  of  the  mother.  Riite,  in  1845,  said,  '  The  defect  is 
hereditary,  and,  peculiarly  enough,  rather  through  the  wo- 
men than  the  men.  For  example :  the  maternal  grandfather 
transmits  to  the  grandchildren.'  A  very  interesting  proof 
of  this  law  I  have  lately  received  by  letter  from  Professor 
Valentine  of  Berne,  Nov.  5,  1878,  who  writes,  '  I  naturally 
can  have  no  opinion  as  to  Horner's  law.  I  only  know  one 
case  near  me  which  supports  it.  Professor  F.,  formerly 
here,  was  color-blind:  his  children  are  not.  He  had  five 
daughters,  who  are  all  married.  Their  children,  so  far  as  I 
could  trace,  are  mostly  color-blind.'  " 

Again  Magnus  says,  — 

"  I  have  also  among  my  color-blind  found  with  certainty 
six  times  that  the  maternal  relatives  were  color-blind,  and 
it  was  inherited  through  them.  In  three  of  these  cases  it 
was  the  mother's  brother,  maternal  uncle,  who  was  color- 
blind. Two  sisters  each  had  a  color-blind  son,  one  of  whom 
I  tested.  Two  cousins,  daughters  of  two  sisters,  each  had 
a  color-bMnd  son.  I  do  not,  therefore,  think  it  too  hasty 
to  say  that  the  color-blind  inherits  his  defect  very  frequently 
from  his  mother's  family.  She  will  be  normal-eyed,  and 
transmit  color-blindness  to  her  sons,  but  not  to  her  daugh- 
ters." 

Besides  the  very  many  times  I  was  told  by  those 


ITS   DANGERS   AXD   ITS   DETECTION.  63 

I  tested  of  some  relative  being  supposed  to  be 
color-blind,  I  had  direct  testimony  from  my  own 
observation,  or  testimony  of  a  character  I  could 
depend  upon,  in  the  following  instances:  Sixteen 
times  brothers  being  color-blind;  once,  father  and 
son ;  maternal  grandfather  and  two  grandchildren, 
boys,  —  three  sisters  not  so  ;  maternal  grandmother 
and  grandson ;  mother  and  son ;  male  cousins 
twice ;  twin  brothers  red-blind ;  of  two  brothers, 
one  red,  the  other  green  blind  ;  a  lad,  his  great- 
uncle  and  grandfather ;  three  brothers  out  of  five 
color-blind,  but  none  of  their  children ;  two  broth- 
ers and  maternal  uncle ;  three  brothers  out  of 
four  color-blind,  the  other  too  young  to  test. 

I  have  thus  called  especial  attention  to  color- 
blindness being  hereditary,  as  it  has  a  direct  bear- 
ing on  the  important  question  of  the  frequency  of 
the  defect,  upon  which  of  course  depends  the  com- 
parative danger  to  the  community  at  large. 


64  COLOR-BLINDNESS 


CHAPTER  VIII. 

PHYSICAL    PECULIAEITIES   CONNECTED  WITH 
COLOK-BLINDNESS. 

I  HAVE  spoken  of  the  improbability  of  the  color 
of  the  iris  or  hair  having  any  connection  with 
color-blindness  other  than  accidental.  My  own 
observations  on  more  than  430  color-blind  induce 
me  to  discard  this  at  present  from  further  thought. 
In  this  Cohn  agrees  with  me.  Where  light  hair 
and  irides  are  in  the  majority  in  the  community, 
they  will  be  so  found  among  the  color-blind. 
Magnus  recorded  48  among  93  color-blind  with 
black,  brown,  or  dark  hair,  and  45  with  blonde  ; 
28  had  yellowish-brown  or  yellowish-gray  eyes, 
and  65  blue  or  bluish-gray.  Seebeck,  in  1837, 
found  10  of  his  12  cases  had  blue  eyes,  but  wisely 
remarks  that  it  is  probably  simply  due  to  the  fact 
that  such  are  most  frequent  among  all  northern 
nations.  There  seems  to  be  nothing  gathered 
from  testing  the  refraction  or  accommodation  of 
color-blind  eyes.  The  results  are  those  to  be 
obtained  from  the  examination  of  the  same  classes 
as  the  color-blind  belong  in.  The  visual  power  is 
apparently  the  same  as  with  the  normal-eyed ;  but 


ITS   DANGERS   AND   ITS   DETECTION.  G5 

I  have  seen  very  extraordinary  visual  power  of 
form  associated  with  color-blindness.  As  to  the 
ear  and  musical  power,  I  can  say  nothing  from  my 
own  observation.  Magnus  could  obtain  nothing 
decisive  on  this  point. 

In  respect  to  parental  relationship,  I  can  only  also 
quote  Magnus  and  Cohn.  The  former,  amongst  his 
94  color-blind,  found  but  six  times  the  parents 
related,  —  always  cousins.  This  point  is  worth 
studying ;  but  deductions  should  be  made  with 
great  caution.  Cohn  also  found  six  times  the 
parents  related.  Five  times  they  were  cousins.  In 
one  case  the  father  had  no  color-blind  children  by 
a  wife  not  related  to  him.  His  second  wife  was 
his  cousin  (their  mothers  being  sisters),  by  whom 
he  had  two  color-blind  sons. 

There  is  one  other  physical  peculiarity  which 
has  been  connected  with  color-blindness ;  and  that 
is  a  contraction  of  the  forehead,  and  consequently 
of  the  anterior  lobes  of  the  brain.  Xiemetscheck 
measured  the  distance  between  the  pupils  of  four 
color-blind,  and  found  it  to  be  49,  50-54  mm. 
From  this  he  deduced  the  idea  that  the  brain  mass 
anteriorily  was  proportionally  smaller ;  and  here 
was  where  the  phrenologists  placed  color-percep- 
tion. The  idea  was  supported  by  Aubert ;  but 
Dr.  Cohn  measured  his  one  hundred  color-blind, 
finding  the  distance  between  the  pupils  thus :  — 

54:-56  mm.  in  20  scholars  9-13  years  old. 
58-62  mm.  in  GO  scholars  9-14  years  old. 
63-66  mm.  in  18  scholars  12-22  years  old. 
67  mm.  in  a  color-blind  67  years  old,  and  70  mm.  in  one 
40  years  old. 

His  conclusions,  therefore,  are  that,  "had  Nie- 


6Q  COLOE-BLINDNESS  : 

metsclieck  found  protrusion  of  the  eyeballs  in  his 
cases,  he  could  as  well  have  connected  it  with 
color-blindness." 

Professor  Pfliiger,  in  Berne,  measured  the  dis- 
tance between  the  pupils  of  1,846  normal-eyed 
children,  and  found  in  those  between  7-14  years 
this  to  be  64-59  mm. ;  in  those  between  15-19, 
to  be  59-62  mm. ;  also,  in  older  students  between 
20-22  years,  he  found  it  was  61-63  mm.  Cohn 
therefore  claims  rightly  that  his  color-blind  had 
rather  a  greater  distance  between  the  pupils  than 
the  normal-eyed  of  the  same  age :  hence  the  theory 
of  Memetscheck  is  not  true. 

Professor  Holmgren  also  reports  in  1878  his 
measurements  of  the  distance  between  the  pupils 
of  100  color-blind.  He  employed  an  instrument 
he  had  specially  arranged  for  this  purpose.  He 
also  finds  that  there  is  no  measurement  of  this 
kind  characteristic  of  the  color-blind. 

Professor  Wilson  said  in  his  book,  — 

"  I  have  to  notice  a  singular  expression  in  the  eye  of  cer- 
tain of  the  color-blind,  which  may  assist  in  their  detection. 
It  is  difficult  to  describe  it,  and  it  is  wanting  in  well-marked 
cases.  But  various  of  the  color-blind,  whose  cases  I  have 
described,  have  presented  a  peculiarity  of  look,  which 
others  have  recognized  on  their  attention  being  drawn  to  it. 
In  some  it  amounted  to  a  startled  expression,  as  if  they 
were  alarmed ;  in  others,  to  an  eager,  aimless  glance,  as  if 
seeking  to  perceive  something,  but  unable  to  find  it  ;  and,  in 
certain  others,  to  an  almost  vacant  stare,  as  if  their  eyes 
were  fixed  upon  objects  beyond  the  limit  of  vision.  The 
expression  referred  to,  which  is  not  at  all  times  equally  pro- 
nounced, never  altogether  leaves  the  eyes  which  it  seems  to 
characterize." 

In  the  appendix  he  also  says,  — 

"  I  have  had  the  opportunity  of  observing  it  somewhat 


ITS   DANGEES   AND   ITS    DETECTION.  b« 

particularly  in  four  gentlemen  not  relatives,  in  two  of  whom 
it  was  readily  recognized  by  others.  All  the  parties  referred 
to  have  healthy  eyes,  and  excellent  vision  for  every  thing 
but  color.  One  has  an  absent,  anxious  glance,  with  some- 
thing of  the  expression  which  amaurosis  gives,  only  the 
pupil  is  small.  One  has  a  startled,  restless  look.  The 
other  two  have  an  eager,  prying,  aimless  air.  The  charac- 
ter common  to  them  all,  and  to  the  other  cases  I  have  seen, 
iy  this  aimlessness  of  look.  Macbeth's  reference  to  Ban- 
quo 's  ghost, — 

'  Thou  hast  no  speculation  in  those  eyes 
Which  thou  dost  glare  with,'  — 

very  happily  expresses  the  peculiarity  which  I  find  so  diffi- 
cult to  define.  It  has  not,  however,  in  most  cases,  any  thing 
repulsive  about  it.  The  majority  of  those  I  have  seen  pre- 
senting it  would  be  described  as  having  fine  eyes.  In  one, 
the  wistful,  somewhat  melancholy,  but  pleasing  expression 
of  his  eye,  had  attracted  my  attention  long  before  I  knew 
that  he  was  color-blind." 

I  can  recall  something  of  what  Dr.  Wilson  de- 
scribes in  reference  to  two  or  three  of  my  color- 
blind acquaintances,  but,  on  the  contrar}^  not  at 
all  in  reference  to  others.  I  recognize  his  difficulty 
of  describing  just  what  it  is.  I  doubt  if  I  should 
have  noticed  it,  or  at  least  connected  it  with  color- 
blindness, except  for  his  remarks  in  reference  to 
it.  Had  he  spoken  of  such  a  look  or  peculiar 
expression  on  the  part  of  the  color-blind  when 
being  examined,  I  could  corroborate  it  from  my 
experience  with  both  adults  and  young  persons. 
I  have  now  and  then  made  m}^  diagnosis  correctly, 
from  a  peculiar  dazed,  half-anxious  expression  of 
the  face  and  eyes  of  a  looker-on  awaiting  his  turn, 
as  if  they  were  called  upon  to  do  something  unu- 
sual, and  sought  or  expected  further  explanation 
than  that  given  the  normal-eyed.     I   do    not,  of 


68  COLOR-BLINDNESS  ; 

course,  mean  the  natural  nervousness  of  those 
conscious  of  some  defect ;  but  of  those  color-blind 
who  had  no  idea  any  thing  was  wrong  with  their 
chromatic  sense,  and  who  often  proved  difficult  to 
convince.  I  believe  no  other  observer  than  Pro- 
fessor Wilson  has  remarked  on  or  recorded  any 
thing  of  the  kind. 

As  to  nationality,  I  have  but  to  sa}^,  that,  in  our 
mixed  population,  nearly  every  European  nation 
is  represented.  An  opinion  was  expressed  long 
ago,  that  the  defect  did  not  occur  in  the  colored 
race.  My  opportunity  of  testing  them  has  been 
but  very  small.  Among  102  colored  schoolboys 
I  found  2  color-blind;  among  94  colored  school- 
girls, none. 

Whilst  this  volume  is  in  press  I  have  heard  from 
Dr.  Swan  M.  Burnett  of  Washington,  D.C.,  who 
has  had  an  opportunity  I  could  not  obtain.  He 
has  tested,  by  Professor  Holmgren's  method,  1,359 
colored  schoolboys,  and  found  22  color-blind  (or 
1.6  per  cent) ;  also  1,691  colored  schoolgirls,  finding 
only  2  color-blind  (or  0.11  per  cent).  This  smaller 
percentage  among  the  boys  may  be  due  to  various 
causes  aside  from  the  difference  of  race.  More- 
over, larger  numbers  may  entirely  change  it. 


ITS  DANGERS   AND   ITS   DETECTION.  69 


CHAPTER  IX. 

FEEQUENCY   OF   COLOR-BLINDXESS   IN"  ISIALES. 

As  the  magnitude  of  the  clanger  depends,  of 
course,  on  the  frequency  of  the  defect,  it  becomes 
important  to  know  in  what  proportion  of  the  com- 
munity color-blindness  is  likely  to  occur.  Very 
variable  statistics  are  given  by  different  observers, 
depending  largely  upan  the  methods  of  testing; 
the  more  thorough  and  scientific  these  latter  are, 
the  greater  being  the  number  of  color-blind  indi- 
viduals found.  Mistakes  of  excessive  ratio  re- 
ported are  now  better  understood  and  avoided, 
since  we  know  color-blindness  runs  in  families, 
and  is  hereditary.  An  observer  might  thus  find 
10  out  of  40  individuals  examined  color-blind. 
Let  us  glance  at  the  statistics,  such  as  they  are, 
reported  by  the  earlier  observers.  Dalton  found 
8  to  12  per  cent ;  Professor  Pierre  Prevost,  3  to  5 
per  cent.  Professor  Kelland  of  the  Edinburgh 
University  found,  among  151  students,  3  "thor- 
ough Daltonians,"  and  several  less  well-marked 
cases.  Wilson  again  found  2  among  20  students, 
1  among  47  other  students;  on  the  Edinburgh 
police,  five  among  158.    Dr.  Rowe,  at  the  Morning- 


70  COLOE-BLINDNESS  : 

side  Asylum,  found  5  among  42  male  attendants. 
These  I  quote  from  Wilson.  Seebeck  found  5 
color-blind  among  100  students.  Professor  Allen 
Thomson  met  with  the  same  result  as  Dr.  Wilson, 
as  also  D'Hombre-Firmas  in  France,  and  Professor 
Dove  in  Berlin.  Dr.  Wilson  also  examined  a 
large  number  of  soldiers,  who,  together  with  those 
above  spoken  of  as  tested  by  him,  amount  alto- 
gether to  1,154  persons.  Amongst  these  all,  Q5 
were  color-blind,  an  average  of  6.6  per  cent,  or 
1  in  17.7.  The  red-blind  were  most  numerous 
throughout  all  these.  This  proportion  has  been 
now  admitted  by  Professor  Helmholtz.  Wilson 
said,  in  1854,  — 

"  The  statistics  of  color-blindness  are  as  yet  very  imper- 
fect, and  do  not  include  females;  but  there  is  every  reason 
to  believe  that  the  number  of  males  in  this  country  (Eng- 
land) who  are  subject  in  some  degree  to  this  affection  is  not 
less  than  1  in  20,  and  that  the  number  markedly  color- 
blind— i  e.,  given  to  mistake  red  for  brown,  brown  for  green, 
purple  for  blue,  and  occasionally  red  for  black  —  is  not  less 
than  1  in  50.  We  may  thus,  according  to  our  present 
knowledge,  regard  two  in  every  hundred  of  the  community 
as  seriously  defective  in  their  perception  of  color." 

Dr.  Goubert  estimates  1  in  25  color-blind. 
Dove,  in  his  memoir  of  1872,  gives  the  following 
figures :  Among  860  men,  there  were  40  color- 
blind, 4.65  per  cent,  or  1  in  21.5 ;  among  611 
women,  5  color-blind,  or  0.82  per  cent,  or  1  to  122. 
Among  1,016  scholars  at  the  Lyons  Lyceum,  he 
found  16  color-blind  for  red  and  green  on  a  visit 
made  in  April,  1877. 

The  last  report  of  Dr.  Favre,  of  the  Lyons 
Mediterranean  Railroad,  gives  the  results  of  ex- 
aminations of  railroad  employes   since    1855.     It 


ITS   DANGEES    AND   ITS   DETECTION.  71 

sliows  also  how  more  careful  tests  discover  a 
greater  proportion  of  color-blind  persons.  Dr. 
Favre,  up  to  1855,  liad  examined  about  5,000  can- 
didates for  railroad-work,  and  rejected  more  than 
50  for  being  red-blind.  He  had  not,  unfortunately, 
kept  accurate  records.  From  1855  to  1864  he 
noted  8  color-blind  only,  which  number  does  not 
correspond  with  the  number  of  men  examined. 
From,  1862  to  1872,  among  1,196  persons,  he  re- 
fused 14  color-blind  who  could  not  tell  red.  From 
May,  1873,  to  July,  1875,  his  examinations  were 
more  particular  and  exact ;  and  he  found,  among 
1,050  persons  seeking  railroad  employment,  98 
who  made  decided  blunders,  or  hesitated :  10  were 
refused  for  being  red-blind.  His  new  series  since 
1875  comprises  600  examinations :  the  results  of 
these  he  has  not  yet  sent  me  (January,  1879). 
728  men  already  in  employment  were  examined  in 
1872-73.  More  than  one-third  of  these  had  been 
previously  tested  for  color,  and  the  red-blind  elim- 
inated. Of  these  728,  42  either  made  mistakes  or 
repeated  hesitations.  Among  224  conductors  ex- 
amined by  Dr.  Favre  and  M.  Git,  14  were  found 
decidedly  color-blind.  In  1874  he  found  4  color- 
blind among  75  office-clerks;  the  same  year,  24 
among  Qfb  firemen  at  the  Perrache  gas-works.  At 
the  Ouillins  works,  among  148  workmen  whom 
he  examined  in  August,  1877,  82  told  the  five 
elementary  colors  without  error  or  hesitation ;  56 
either  hesitated  or  made  mistakes.  May  7,  1877, 
among  155  students  at  the  veterinary  school  at 
Lyons,  Dr.  Favre  found  19  hesitate  or  make  mis- 
takes. Examining,  with  Capt.  Bellecour,  268  sub- 
officers  and  men  of  the  Sixteenth  line,  he  found 


72  COLOR-BLINDNESS  : 

105  color-blind  or  color-deficient.  Among  138 
men  of  the  Twenty-second,  Twenty-third,  and 
Ninety-ninth  line,  M.  Paul  Guillot  found  37  color- 
blind. Lieut.  Gallet  of  the  Twenty-sixth  Artil- 
lery, in  garrison  at  Mans,  examined  116  young 
soldiers,  and  found  32  who  hesitated  or  made  mis- 
takes on  a  color-scale  of  15  shades.  Lieut.  Lau- 
theaume  found  40  color-blind  among  132  men  of 
the  train  of  the  Twenty-sixth  Artillery.,  The 
average  among  this  series  of  654  young  soldiers 
was  32.72  per  cent.  Dr.  Mourand,  among  200 
men  of  the  Lyons  station,  found  7  color-blind. 
Dr.  Favre  says  his  colleague  must  have  noted 
only  the  most  marked  cases. 

Dr.  Feris,  in  his  pamphlet,  and  more  recently  in 
a  communication  to  Dr.  Favre,  reports  having  ex- 
amined 775  officers  and  sailors,  amongst  whom  he 
found  75  color-blind  :  19  wholly  confounded  red 
and  green.  The  average  of  this  series  is  10  in  100. 
Of  all  the  adults  Dr.  Favre  examined,  the  average 
was  16.84  to  100.     He  says,  — 

"  The  results  will  vary  greatly,  being  dependent  on  many 
circumstances  and  peculiarities  I  shall  hereafter  notice  ;  but 
we  may  be  assured,  that  in  France  the  color-blind  amount 
to  ten  in  one  hundred  of  the  adult  males.  .  .  .  The  study  of 
color-blindness  interests  at  least  a  tenth  of  our  population 
(France).  This  very  large  proportion  gives  us  the  measure 
of  the  chances  of  error  the  color-blind  run  in  the  various 
industries  where  good  color-perception  is  necessary  or  use- 
ful. It  does  not,  of  course,  give  us  an  exact  idea  of  the 
chances  of  accident  at  sea  and  on  railroads,  on  account  of 
the  accessory  circumstances  which  aid  the  color-blind  in  his 
embarrassment ;  but  it  shows  us  plainly  how  numerous  the 
chances  are." 

Dr.  Favre  also  reports  the  results  he  received 
from  a  friend  in  Algiers,  who  tested,  with  great 


ITS   DANGERS   AND   ITS   DETECTION.  73 

care,  693  persons,  and  found  as  follows :  Among 
203  Kabjles,  5  cases  of  color-blindness;  in  95  Bis- 
kris,  4  cases ;  in  81  negroes,  1  case ;  in  23  Jews,  1 
case  ;  in  15  Spaniards,  none  ;  in  62  Italians,  1  case  ; 
in  15  Mozabites,  none  ;  in  12  Maltese,  1  case ;  in  8 
Tunisians,  none  ;  in  19  Europeans,  1  case,  —  in  all, 
19  cases  among  693  persons  examined,  or  2.75  per 
cent. 

Dr.  A.  Lederer  has  lately  found  63  color-blind 
persons  amongst  1,312  men  of  the  Austrian  navy, 
or  4.8  per  cent. 

Dr.  Fontenoy  found  31  color-blind  out  of  1,084 
railroad  employes  of  Denmark,  or  2.87  per  cent. 

Professor  Donders  of  Utrecht,  Holland,  found, 
among  2,300  railroad  employes,  152  color-blind. 

Dr.  Stilling  of  Cassel,  Germany,  found,  out  of 
400  railroad  employes,  6  per  cent  color-blind. 

Dr.  Krohn,  in  Finland,  found,  among  1,200  rail- 
road emplo3'es,  60,  or  5  per  cent  color-blind.  These 
and  other  reports  of  railroads  I  shall  return  to 
hereafter. 

Professor  Quaglino  of  Milan,  Italy,  writes  me 
(Aug.  11,  1877),— 

"It  has  been  generally  believed  that  color-blindness  is 
more  rare  in  Italy  than  in  Germany,  England,  or  France ; 
but  I  much  doubt  this,  as  there  has  been  little  research 
among  us,  and  I  think  that  a  large  amount  will  be  found 
were  it  carefully  looked  for." 

Dr.  Daae  of  Kragero,  Norway,  found,  amongst 
205  schoolboys,  4.88  per  cent  color-blind. 

Dr.  Cohn  found,  among  2,429  schoolboys  of 
Breslau,  95  or  4  per  cent  color-blind. 

Dr.  Magnus  found,  among  3,273  Breslau  school- 
boys, 3.5  per  cent  color-blind. 


74 


COLOR-BLINDNESS 


Professor  Holmgren,  in  Sweden,  found,  among 
32,165  males,  1,019,  or  3.25  per  cent  color-blind. 

Dr.  Minder  of  Berne,  Switzerland,  found,  among 
1,429  males,  95,  or  6.58  per  cent  color-blind. 

To  recapitulate  the  larger  numbers  and  more 
recent  examinations :  — 


Observers. 

Place. 

II 

Position  in  Life. 

p 

d  W 

S  1" 

^ 

^ 

fu 

Dr.  Fontenoy    . 

Copenhagen    . 

1,084 

31 

2.87 

Eailroad  employes. 

Prof.  Donders    . 

Utrecht    .        . 

2,300 

152 

6.60 

<(               <( 

Dr.  Krohn . 

Finland    . 

1,200 

60 

5.00 

<<               (( 

Dr.  Minder 

Berne 

1,429 

95 

6.58 

Schools  and  various. 

Dr.  Daae    . 

Norway  . 

205 

- 

4.88 

Schoolboys. 

Dr.  Cohn    . 

Breslau    . 

2,429 

95 

4.00 

<< 

Dr.  Masnus 

3,273 

3.50 

« 

Dr.  Stilling 

Cassel      .        '. 

400 

_ 

6.00 

Railroad  employes. 

Dr.  von  Reuss   . 

Vienna     . 

800 

_ 

3.50 

Railroad  employes. 

Prof.  Holmgren, 

Sweden    . 

3,654 

166 

4.54 

Scholars. 

< 

8,082 

300 

3.45 

" 

< 

1,523 

47 

3.08 

Students. 

' 

2,752 

105 

3.81 

Orphan  children. 

' 

555 

43 

4.50 

Young  people. 

« 

7,953 

171 

2.15 

Railroad  employes. 

« 

4,225 

94 

2.22 

Sailors. 

< 

1,851 

62 

3!34 

Soldiers. 

< 

649 

31 

4.77 

Mill-hands. 

" 

321 

18 

5.60 

Prisoners  and  g'rds. 

Dr.  Jeffries 

New  England, 

10,387 

431 

4.149 

Teachers  and  sch'rs. 

The  following  are  the  results  in  tabular  form  of 
my  own  examinations :  — 


ITS  BANGERS  AXD   ITS   DETECTION. 


75 


H 

Iff  II'  1 

§''          s 

S" 

Sr- 

1 

Instructors  and  Students. 

Several  departments  of  Harvard  University,  Cambridcrn, 
Mass.;  Institute  Techiiolo.i,'y,  Boston,  Mass. ;  Amherst  Col- 
lege, Mast?. ;  Brown  University,  I'rovidencc,  R.I.  . 

Teachers'  and  Students'  State  Art-School 

Other  adults 

1 

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o 

m 

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J 

76  COLOR-BLINDKESS  : 

All  these  examinations  were  made  by  Holm- 
gren's method  with  the  colored  worsteds,  to  be  de- 
scribed later  in  this  volume.  The  division  into  red 
and  green  blindness  of  the  first  thirty-five  hundred, 
I  am  not  as  sure  of  as  that  of  those  afterwards, 
for  reasons  I  have  stated  in  my  last  chapter.  I 
have  followed  Professor  Holmgren,  and  my  results 
correspond  very  nearly  with  his  and  those  of 
observers  who  have  also  been  governed  by  his 
directions. 

My  work  so  far  has  been  rather  the  collection  of 
statistics,  and  the  dissemination  of  a  knowledge 
of  color-blindness,  than  a  study  of  the  defect  itself, 
except  in  individual  cases.  I  am,  therefore,  merely 
presenting  its  frequency  here,  which  can  as  well  be 
determined  from  school-children,  since  a  person 
born  color-blind  dies  so. 

My  friend.  Dr.  Magnus  of  Breslau,  from  his 
own  and  Professor  Cohn's  reports  of  their  exami- 
nations of  the  school-children  above  quoted,  con- 
cludes that  color-blindness  is  more  frequent  as  we 
descend  the  social  scale,  and  also  more  frequent 
amongst  the  Jews.  As  to  this  last  I  was  unable 
to  decide  whether  the  schoolboys  were  Jews  or 
not.  In  regard  to  the  former,  —  viz.,  the  greater 
frequency  among  the  lower  classes,  —  I  was  sur- 
prised to  find  this  did  not  hold  in  our  community 
of  mixed  races,  nor  did  it  among  the  schools  where 
the  race  was  more  purely  American.  Parentage 
I  could  not  record;  but,  in  a  general  way,  I  should 
say  the  percentage  would  be  as  high  or  higher 
among  American-born  children.  My  work  has 
satisfied  me  that  we  cannot  draw  safe  deductions 
from  a  few  thousand  examinations,  but  must  pa- 


ITS   DAXGEES   AND   ITS   DETECTION.  7( 

tiently  wait  till  our  lists  contain  enough  to  elimi- 
nate sources  of  error  from  inadequate  data  and,  so 
to  speak,  possible  local  causes. 

I  have  made  no  column  of  violet-jellow-blind- 
ness,  as,  besides  some  very  doubtful,  I  can  but 
report  three  cases ;  and  these  I  have  allowed  to  be 
recorded  under  "  partially  color-blind."  These 
tliree  cases  I  carefully  examined  again,  and  found 
that  whilst  the  red-green  perception  was  not,  per- 
haps, perfect, — so  that,  on  that  account,  they  would 
propably  have  been  classed  among  the  "  partially," 
— yet  as  to  violet  yellow  they  were  wholly  blind,  as 
shown  by  Holmgren's  worsted  test.  In  one  case 
there  was  reduced  color-perception  for  all  three 
of  the  primary  colors,  —  red,  green,  and  violet.  I 
have  no  doubt,  that,  to  many  of  my  color-blind, 
the  spectrum  would  be  more  or  less  shortened  at 
the  violet  end.  Many  were  too  young  to  thus  test, 
and  that,  moreover,  was  not  the  purpose  of  my 
work  at  the  time  of  examination. 

I  should  add  here  that  I  made  no  examination 
or  record  of  the  exact  visual  power  for  form  of  the 
color-blind  I  found,  as  it  is  wholly  uncalled  for  by 
this  method  of  testing.  They  were  teachers,  stu- 
dents, or  scholars  at  work  with  their  eyes.  Nei- 
ther did  I  have  to  regard  whether  they  were  nor- 
mal-eyed, old-sighted,  near-sighted  or  over-sighted 
(presbyopic,  myopic,  or  hypermetropic),  since  we 
need  not  correct  errors  of  the  refraction  of  the 
eye  when  thus  searching  for  color-blindness. 

I  have  not  given  the  percentage  of  the  thirty- 
one  "other  adults,"  as  some  came  to  me  suspecting 
or  knowing  of  their  defect.  There  were,  however, 
only  three  of  these.     The  others  were  accidental 


78  COLOR-BLINDNESS  : 

examinations  amongst  acquaintances  or  patients 
and  employes.  I  omit  also  the  special  percentage 
of  the  art-school. 

The  instructors  and  students  of  the  colleges  I 
have  added  together,  to  better  eliminate  sources  of 
errors,  as  I  did  not  examine  all  the  students  of  any 
one  of  these  institutions. 

In  the  statistical  memoirs  of  the  United  States 
Sanitary  Commission,  published  in  1869,  are  the 
only  other  examinations  I  know  of  made  in  this 
country.  The  method  of  testing  —  viz.,  holding  up 
pieces  of  colored  cloth,  &c.,  and  asking  the  names 
of  the  color  —  was,  of  course,  very  crude  and  un- 
reliable. I,  however,  introduce  the  report  here. 
The  compiler,  Dr.  B.  A.  Gould,  says,  — 

"  Serious  misunderstandings  or  calamities  have  been  re- 
ported in  the  army,  resulting  from  mistakes  in  the  color  of 
green  and  red  lights  by  officers  of  the  signal  corps,  them- 
selves not  fully  aware  of  their  failing  in  this  respect  ;  and 
cases  have  occurred  when  ludicrous  and  even  disastrous  re- 
sults have  followed  the  use  of  a  badge  of  precisely  the 
wrong  color." 

Instructions  were  issued  to  test  for  color-blind- 
ness ;  and,  in  the  reports  received,  "  the  descrip- 
tions of  the  irregularities  manifested  in  distinguish- 
ing colors  are,  in  general,  neither  complete  nor 
adequate,  owing  propably  to  insufficiency  of  the 
instructions  given."  Among  8,831  white  men, 
161  were  found  color-blind,  equal  to  0.02.  This 
small  ratio  is,  of  course,  due  to  the  crude  method 
of  examining,  which  would  only  detect  the  most 
marked  cases  of  color-blindness.  Dr.  Gould 
adds,  — 

"  Notwithstanding  the  incompleteness  of  the  descriptions 
returned,  and  the  consequent  inadequacy  of  the  classifica- 


ITS   DAXGEES   AisD   ITS   DETECTION.  79 

tion,  the  well-known  fact  is  distinctly,  manifest,  that  the 
most  usual  form  of  color-blindness  is  that  -which  fails  to  dis- 
tinguish between  the  green  and  red,  and  that  the  confusion 
of  colors  sometimes  embraces  the  other  half  of  the  spec- 
trum, and  sometimes  its  entire  range." 

The  great  yariation  in  the  ratio  of  color-blind 
persons,  reported  by  different  observers,  is  readily 
explained  by  differences  in  the  accuracy  of  the 
method  of  testing. 

In  testing  color-perception  by  the  sun's  spec- 
trum thrown  on  a  white  surface,  the  color-blind 
observer  will  see  the  color  he  is  deficient  in  over 
a  smaller  surface.  Dr.  Edward  Rsehlmann,  in 
Halle,  reports  the  test  of  70  people  with  the  sun's 
spectrum.  He  found  only  30  of  them  saw  the 
red  normally:  the  others  varied  in  their  red-per- 
ceptive power.  He  tested  only  20  as  to  the  violet 
end  of  the  spectrum,  and  found  remarkable  short- 
ening of  the  visible  portion  for  this  end  also.  He 
noticed,  besides,  that,  when  the  red  end  of  the 
spectrum  was  shortened,  the  violet  was  also  re- 
duced, limiting  the  spectral  row  of  colors  on  both 
ends. 


80  COLOR-BLINDNESS : 


CHAPTER  X. 

rNFREQUENCY  OF  COLOR-BLINDNESS  IN  FEMALES. 

In  an  article  written  in  December,  1877,  on  the 
dangers  of  color-blindness,  and  published  in  the 
Ninth  Annual  Report  of  the  Massachusetts  State 
Board  of  Health,  I  stated,  — 

"  It  has  been  frequently  said  that  color-blindness  was  less 
common  among  females  than  males.  This  is  prohabhj  incor- 
rect, and  due  to  the  fact  that  such  a  defect  is  of  more  im- 
portance with  the  female  sex,  and  therefore  more  carefully- 
concealed.  They  have  not  been  tested  as  males  have ;  and 
most  likely  future  statistics,  based  on  true  methods  of  test- 
ing, will  reverse  the  now  quite  general  impression  as  to  their 
having  better  color-perception,  and  hence  to  be  preferred, 
where  admissible,  as  railroad  employes." 

My  doubt  was  also  based  upon  the  fact  that  we 
then  had  no  large  number  of  reliable  statistics  to 
prove  the  contrary,  but  more  especially  because 
methods  of  testing  for  color-blindness  in  females 
had  been  employed,  calling  upon  the  observed  to 
name  colors  shown,  which  females,  from  habit, 
could  unquestionably  do  with  greater  facility  than 
men;  and  hence  fewer  appear  deficient  in  color- 
perception.  Professor  Wilson,  in  his  "  Researches 
on  Color-Blindness,"  says  (p.  75), — 


ITS   DANGERS   AND   ITS   DETECTION.  81 

"  I  have  no  results  to  offer  respecting  the  prevalence  of 
color-blindness  among  females.  I  have  already  stated  my 
conviction  that  it  is  rarer  among  them  than  among  males ; 
but  only  an  extended  inquiry  can  show  the  amount  of  differ- 
ence in  this  respect  between  the  sexes." 

In  a  note  in  his  Appendix  (p.  164),  he  adds,  — 

"  Since  the  text  was  written,  I  have  been  informed  of  a 
few  more  cases  of  color-blindness  among  educated  women 
in  England.  The  general  tendency,  however,  of  my  later 
inquiries,  as  of  my  earlier  ones,  is  to  show  that  color-blind- 
ness is  very  much  rarer  among  women  than  men." 

Dr.  A.  Favre,  in  an  article  in  the  "  Gazette 
Hebdomadaire,"  Oct.  12,  1877,  says, — 

"  We  have  tested  very  few  adult  females,  from  the  diffi- 
culty of  such  examinations,  but  more  especially  because  the 
majority  of  women  readily  acquire  an  exact  notion  of  colors, 
and  they  do  not  belong  to  the  professions  wh^re  color-blind- 
ness is  dangerous  :  hence  they  do  not  interest  us  more  in  an 
industrial  than  a  medical  point  of  view.  Among  236  girls 
of  four  schools  (three  in  Lyons,  one  in  Paris),  we  found  8 
children  only  who  made  serious  mistakes;  namely,  3.o9  per 
cent.  In  the  '  salles  (Tasiles '  and  the  infant-schools  the  errors 
were  as  frequent  among  the  little  girls  as  boys." 

It  must  be  remembered  that  Dr.  Favre  reported 
an  enormous  number  of  children  of  both  sexes  as 
color-blind;  but  he  tested  them  by  asking  the 
names  of  the  colors  of  objects  held  up  before 
them.  He  found,  as  may  be  readily  imagined, 
many  of  the  youngest  children  of  both  sexes  una- 
ble to  answer  correctly ;  whilst,  among  the  older 
children,  the  girls  had  naturally  learned  the  names 
')f  colors  better  than  the  boys.  This,  I  think,  is 
all  that  his  test  proves,  as  I  shall  hereafter  show. 

In  1860  Dr.  Henri  Dor  of  Berne  tested  in  Berlin 
611  women,  using  a  method  similar  to  that  of  Pro- 
fessor Holmgren;  namely,  the  sorting  of  colored 


82  COLOR-BLINDNESS  : 

worsteds,  with  the  result  of  finding  only  5  —  or 
0.82  per  cent,  or  1  in  122  —  color-blind.  This 
method  does  not  call  upon  the  examined  to  name 
a  color;  and  the  eye  alone,  not  memory,  guides 
the  hand.  Its  value  is  shown  by  the  results  it 
gave.  Perhaps  these  investigations  of  Dor  should 
have  prevented  my  doubting  the  less  frequent 
occurrence  of  color-blindness  in  women  than  men. 
They  seemed,  however,  to  stand  somewhat  alone, 
and  not  sufficiently  extended. 

Professor  Holmgren,  in  his  recent  work  on  color- 
blindness, touches  on  this  jDoint ;  and,  as  his  expe- 
rience renders  what  he  says  of  special  value,  I 
quote  his  remarks :  — 

"  In  drawing  conclusions  from  the  statistics  of  the  exam- 
ination of  women  hitherto  made,  w^e  must  first  of  all  ascer- 
tain if  the  method  of  testing  was  such  that  the  previous 
occupation  of  the  examined  had  not  affected  the  results 
obtained.  For  if  the  method  was  based  on  the  principle  of 
asking  the  names  of  the  colors  of  objects  exhibited,  and  the 
chromatic  sense  of  the  person  examined  judged  by  the  reply, 
then  it  is  very  evident  that  the  proportion  of  color-blind  will 
appear  less  with  women  than  men.  Admitting  that  color- 
blindness is  less  common  in  women  than  men,  we  are  by  no 
means  justified  in  attributing  this  to  their  greater  familiarity 
or  exercise  with  colors.  If  exercise  can  have  any  such  influ- 
ence, it  cannot,  as  we  have  seen,  cure  the  individual,  but 
rather  affect  the  offspring,  as  employment  insensibly  affects 
future  generations.  The  laws  of  heredity  are  too  little 
known  to  allow  us  to  indicate,  or  even  conjecture,  how  this 
takes  place;  but  we  do  know  with  certainty  that  good  quali- 
ties as  v/ell  as  defects  are  transmitted,  and  amongst  the 
latter  we  may  include  color-blindness.  AVe  believe,  more- 
over, that  the  exercise  of  a  sense  may  favorably  affect 
heredity,  although  it  is  difficult  for  us  to  prove  this." 

At  the  present  moment  observers  in  Europe  are 
testing  this  question  of  the  relative  color-blindness 


ITS   DANGERS   AXD   ITS   DETECTION.  83 

of  the  two  sexes.  Their  results,  where  Professor 
Holmgren's  method  has  been  employed,  are  of 
great  value.  A  number  of  reports  of  this  character 
have  come  to  my  hand.  Dr.  E.  Hansen  of  Copen- 
hagen found  none  color-blind  among  50  female 
railroad  emyloyes.  Dr.  A.  Daae  of  Kragero,  Nor- 
way, also  used  Holmgren's  method  with  the  wor- 
steds in  examining  413  school-children  of  both 
sexes,  from  nine  to  fifteen  years  of  age.  Amongst 
208  girls  he  found  none  color-blind,  and  only  5  with 
imperfect  color-perception.     He  says,  — 

"The  better  color-perception  of  the  girls  than  the  boys 
was  very  marked.  Is  this  because  the  girls  have  personally 
more  exercise  with  colors  than  the  boys?  If  this  is  the 
case,  then  vre  must  assume  that  even  very  considerable  de- 
grees of  color-blindness  may  be  relieved  by  many  years' 
exercise.  This  is,  however,  not  probable.  It  is  more  prob- 
able that  the  better  color-perception  which  the  female  sex 
has  acquired  and  developed  by  many  generations  of  handling 
colored  objects  is  essentially  sexual,  or  only  inherited  by 
the  female  descendants." 

Since  February,  1878,  when  I  published  an  arti- 
cle on  the  incurability  of  congenital  color-blind- 
ness, my  experience  with  intelligent  and  educated 
persons  thus  afflicted  has  fully  substantiated  what  I 
then  said;  nan^ely,  that  it  has  not  been  and  cannot 
be  cured  by  exercise  with  colors.  The  color-blind 
reported  to  me  their  futile  attempts  to  do  this,  as 
others,  for  instance,  reported  to  Professor  Wilson 
years  ago,  and  to  Professor  Holmgren  more  re- 
cently. Greater  familiarity  with,  and  more  con- 
stant use  of,  colors  on  the  part  of  females,  seems 
at  first  sight  to  explain  their  somewhat  extraor- 
dinary exemption  from  color-blindness  as  compared 
with  males.     This  does  not,  however,  affect  the 


84  COLOR-BLINDNESS  : 

individual.  Whether  the  individual  is  influenced 
through  generations  of  female  ancestors  exercised 
with  colors,  I  must  for  the  present  leave  with  Mr. 
Darwin,  Mr.  Wallace,  and  Mr.  Grant  Allen  to 
discuss.  The  transmission  of  the  defect  in  the 
male  line  alone  is  very  frequent.  But  there  are 
cases  of  even  the  reverse  on  record.  Dr.  Pliny 
Earle  reported,  out  of  61  relatives,  —  32  males  and 
29  females,  —  20  cases  of  color-blindness,  tivo  of 
these  being  females.  Again  I  would  recall  Cunier's 
case  of  a  lady  who  was  color-blind.  Her  mother 
and  two  sisters  were  the  same.  Her  brother  was 
free  from  the  defect.  The  lady  had  six  children, 
—  one  son  not  color-blind,  and  five  daughters 
affected  like  herself.  The  oldest  daughter  had 
four  children,  —  two  of  them  girls,  color-blind. 
The  second  daughter  had  a  boy  and  girl,  the  latter 
color-blind.  The  fourth  daughter,  unmarried.  The 
fifth  left  a  boy  myopic,  but  not  color-blind.  We 
thus  have  the  remarkable  instance  of  color-blind- 
ness appearing  07ily  in  the  females  of  a  family  for 
four  generations.  Heredity  has  here  apparently 
acted  Avithout  reference  to,  or  directly  against,  the 
accumulated  effects  of  generations  of  exercise  with 
colors.  It  is  certainly  a  very  curious  fact,  that,  if 
generations  of  exercise  with  colors  is  gradually 
eliminating  color-blindness  from  females,  this 
should  not  have  checked  its  transmission  through 
females  exclusively  for  four  generations. 

But  to  return  again  to  the  reports  I  have 
received  from  European  gentlemen :  Dr.  Cohn 
found  among  1,061  Breslau  schoolgirls  none  color- 
blind. Dr.  Magnus,  in  Breslau,  found  but  1  color- 
blind girl  among  2,216. 


ITS   DANGEPwS   AND   ITS   DETECTION. 


85 


Professor  Holmgren  reports  from  Sweden  having 
found,  among  7,119  females  of  all  ages,  19,  or  0.26 
per  cent,  color-blind. 

Dr.  Minder,  in  Berne,  reports,  among  846  girls 
and  women,  having  found  11  color-blind,  or  the 
very  large  per  cent  of  1.3. 

To  recapitulate  from  a  number  of  observers,  — 


Observee. 

Country. 

1 

a 

1 

^ 

Position  of  Persons 

3 

D 

^ 

Tested. 

^ 

^ 

^ 

Dr.  Dor     . 

Berlin      . 

611 

5 

.82 

Working-Tvomen. 

Dr.  Fontenoy    . 

Copenhagen    . 

50 

0 

- 

Railroad  employes. 

Dr.  Magnus 

Breslau    . 

2,216 

1 

.04 

Schoolgirls. 

Dr.Colin  .        . 

" 

. 

1,061 

0 

— 

«« 

Dr.  Minder 

Berne 

, 

846 

11 

1.30 

« 

Prof.  Holmgren, 

Sweden 

• 

3,244 
1,374 

9 
3 

.27 
.21 

School-children. 

" 

<« 

, 

97 

3 

3.09 

Confirmed. 

" 

" 

. 

1,826 

3 

.16 

Factory-girls. 

" 

" 

. 

524 

1 

.19 

Railroad  attendants. 

" 

«« 

. 

51 

0 

_ 

Old  women. 

Dr.  Jeffries. 

Boston 

• 

7,942 

4 

.052 

Students  and  scholars. 

r  My  want  of  success  in  finding  more  color-blind 
females  would  have  at  first  rendered  me  doubtfid 
of  my  testing ;  but  that  was  not  the  case  when  I 
commenced  with  females.  I  have  often  thought 
that  I  had  found  a  case;  but  was  quickly  con- 
vinced, as  were  the  bystanders,  that  it  would  not 
stand  the  test,  and  was  but  the  result  of  nervous- 
ness, carelessness,  or  stupidity.  Females  work  so 
rapidly  in  sorting  the  worsteds,  that  the  examiner 
will  notice  immediately  the  slightest  hesitation  or 
mistake,  as  do  also  those  who  are  waiting  their 
turn.  The  excessive  ratio  reported  by  Dr.  Minder 
of  Berne,  T  cannot  but  think,  may  be  due  to  a  lack 
of  practical  familiarity  with  the  use  of  Professor 
Holmgren's  test  with  females.     He  admits  that,  in 


m  COLOR-BLINDISrESS  : 

cases  he  thought  most  perfect,  the  girl  was  subse- 
quently proved  to  have  been  pickmg  out  only  the 
"  most  brilliant  colors."  This  I  have  seen  often 
enough  among  school  girls  as  well  as  boys.  As  I 
have  elsewhere  said,  it  is  most  curious  how  care- 
lessness and  stupidity  will  at  first  simulate  color- 
blindness; and  if  we  do  not  push  on  with  the 
test  long  enough,  and  be  on  our  guard,  we  may 
quite  readily  mark,  as  at  least  partially  color-blind, 
females  who  are  really  not  deficient  in  chromatic 
sense.  Besides  those  in  my  records,  I  know  of  two 
or  three  color-blind  females,  and  of  two  families 
who  have  color-blind  female  members.  A  natural 
delicacy  and  sensitiveness  render  research  often 
difficult  or  impossible.  In  time  this  peculiarity 
of  vision  will  be  found  too  common  to  be  regarded 
as  a  defect,  much  as  near-sightedness  now  is ;  and 
then  investigations  of  heredity  will  be  more  easily 
carried  out.  At  present  it  is  hardly  understood 
and  appreciated  even  amongst  physicians,  much 
less  amongst  the  laity,  though  interested  per- 
sonally. 


ITS    DANGERS   AND   ITS   DETECTION. 


87 


The  following  table  gives  my  own  results  with 


adults  and  schoolgirls 


11 

e 

Completely. 

'6 
11 

&6 

1 

Position  of 
Persons  Tested. 

< 

rii 

(Sg 

55 

Fi  male    students    of 
Wellesley  College, 
liass. 

Students  of  State  Art- 
School     . 

Girls  of  the  Public 
Schools  of  Boston. 

Normal 

Latin   .... 
High    .... 
Roxbury  High   . 
Dorchester  High 
Charlestowu  High     . 
West  Roxbury  High, 
Brighton  High   . 

Grammar  Schools. 

Bowditch  Grammar  . 
Bowdoin  Grammar   . 
Hancocls  Grammar    . 
Wells  Grammar 
Exeter-st.  Grammar, 
Sherwin  Grammar     . 
Andrew  Grammar     . 
Winthrop  Grammar  . 
Dearborn  Grammar  . 
Comins  Grammar 
Dillaway     . 
Shurtleff     . 
Gaston 
Korcross     . 

- 

302 
84 

123 
63 

796 
43 
39 
89 
42 
35 

341 
398 
486 
451 
90 
500 
215 
963 
407 
348 
332 
653 
411 
731 

Yo 

WOl 

Ad 

■■'2 

13  t 
18  t 

14  t 

8t( 

! 
, 

ung 
nen 

ults. 

0 

olS 
ol9 
o  18 

>15 

1 

1 

1 
1 

1 

1 

_ 
1 

1 

~ 

Total    .        .        . 

- 

7,942 

- 

1 

1 

2 

4 

.052 

88  COLOR-BLINDNESS : 


CHAPTER  XI. 

CONCEALMENT    OF    COLOE-BLINDNESS    LN"  PRACTI- 
CAL  LIFE. 

Such  statistics  as  I  have  given  as  to  the  fre- 
quency of  color-blindness  may,  perhaps,  fairly  chal- 
lenge criticism,  and  it  be  asked.  If  this  is  the 
truth,  how  is  it  that  such  a  chromatic  defect  is 
generally  unknown  or  concealed?  Sir  J.  F.  W. 
Herschel,  in  1859,  when  commenting  on  Mr.  Pole's 
description  of  his  own  color-blindness,  remarked,  — 

"  I  may  be,  perhaps,  allowed  to  add  a  few  words  as  to  the 
statistics  of  this  subject.  Dr.  Wilson  gives  it  as  the  result 
of  his  inquiries,  that  one  person  in  every  eighteen  is  color- 
blind in  some  marked  degree,  and  that  one  in  fifty-five  con- 
founds red  with  green.  Were  the  average  any  thing  like 
this,  it  seems  inconceivable  that  the  phenomenon  of  color- 
blindness should  not  be  one  of  vulgar  notoriety,  or  that  it 
should  strike  almost  all  uneducated  persons,  when  told  of 
it,  as  something  approaching  to  absurdity.  Nor  can  I  think 
that  in  military  operations  (as,  for  instance,  in  the  placing  of 
men  as  sentinels  at  outposts)  the  existence,  on  an  average, 
of  one  soldier  in  every  fifty-five  unable  to  distinguish  a 
scarlet  coat  from  green  grass,  would  not  issue  in  grave  in- 
convenience, and  ere  this  have  forced  itself  into  prominence 
by  producing  mischief.  Among  the  circle  of  my  own  per- 
sonal   acquaintance,    I   have   only   known   two,  though,   of 


ITS   DANGERS   AND   ITS    DETECTION.  89 

course,  I  have  heard  of,  and  been  placed  in  correspondence 
vrith,  several ;  and  a  neighbor  of  mine,  who  takes  great 
delight  in  horticulture,  and  has  a  superb  collection  of  exotic 
flowers,  informs  me,  that,  among  the  multitude  of  persons 
who  have  seen  and  admired  it,  he  does  not  recollect  having 
met  with  one  who  appeared  incapable  of  appreciating  the 
variety  and  richness  of  the  tints,  or  insensible  to  the  bril- 
liancy of  the  numerous  shades  of  red  and  scarlet.  It  may 
be,  however,  that  the  percentage  is  on  the  increase.  Cer- 
tainly we  hear  of  more  cases  than  formerly ;  but  this  proba- 
bly arises  from  the  fact  of  this,  like  many  other  subjects, 
being  made  more  generally  matter  of  conversation." 

I  introduce  these  remarks,  as  they  very  well 
illustrate  the  general  position  of  scientific  men  — 
aside,  of  course,  from  physiologists  —  in  reference 
to  color-blindness.  This  has  continued  pretty 
much  the  same  till  within  the  last  three  years; 
when  methods  of  testing  have  been  used,  so  simple, 
so  rapid,  and  so  convincing,  as  to  enable  us  to 
gather  reliable  statistics  on  a  very  large  scale,  and 
detect  and  expose  the  color-blind  against  their  own 
belief  as  well  as  that  of  others. 

It  must,  however,  be  shown  how  the  color-blind 
have  heretofore,  and  do  now,  escape  detection  in 
the  everj^-day  walks  of  life.  This  will,  at  the 
same  time,  give  us  a  clearer  idea  of  the  peculiari- 
ties of  this  chromatic  defect,  and  clear  up  some  of 
its  seeming  mysteries.  In  the  first  place,  I  must 
call  especial  attention  to  the  very  great  ignorance 
of  the  common  7iames  of  colors  among  the  normal- 
eyed  below  the  well-educated  class  in  the  commu- 
nity, and  the  very  general  misuse  of  the  names  of 
colors  known  or  remembered.  This  I  have  seen 
to  such  an  extent  in  the  thousands  of  school-chil- 
dren I  have  tested,  as  to  excite  the  wonder  and 
even   incredulity   of    the    teachers   watching   my 


90  COLOR-BLINDNESS  : 

work.  Repeatedly  an  instructor  has  wanted  to 
mark  a  boy  color-blind  because  he  so  utterly 
failed  in  designating  colors,  or  even  using  their 
names,  when  ni}^  test  proved  conclusively  that  he 
had  normal  chromatic  perception.  It  convinced 
those  interested  of  the  great  necessity  of  teaching 
colors  and  their  names  in  the  primary  schools,  as 
part  of  educational  work.  Now,  the  color-blind 
simulate  just  this  sort  of  ignorance  in  every-day 
life,  and  hence  are  concealed,  or  escape  detection, 
through  the  want  of  education  of  the  normal-eyed. 

There  is  no  greater  subject  of  dispute  than  the 
question  of  color.  Hardly  any  two  people  will 
agree  as  to  names  of  certain  given  colors.  This  is 
often  a  source  of  amazement  and  amusement  to 
the  color-blind,  who  naturally  think,  that,  if  there 
is  such  doubt  as  to  colors  and  names,  their  own 
doubts  and  mistakes  arise  from  the  same  cause. 
Many  persons  have  been  indignant  with  me  for 
marking  them  as  deficient  in  color-perception,  so 
assured  were  they  that  they  lacked  only  names,  and 
this  even  when  a  most  amusing  and  convincing 
proof  of  their  defect  was  before  the  bystanders. 
Dalton  long  ago  spoke  of  this.  He  says,  when 
speaking  of  three  of  his  pupils,  whom  he  found 
like  himself,  "They,  like  all  the  rest  of  us  color- 
blind, were  not  aware  of  their  actually  seeing 
colors  different  from  other  people,  but  impgined 
there  was  great  perplexity  in  the  names  ascribed 
to  particular  colors." 

Mr.  Prior,  in  "  Nature,"  Dec.  12,  1878,  says,  as 
to  the  general  inaccuracy  of  the  names  of  colors, 
and  the  unfixed  character  of  language,  "I  took 
to  a  flower-show  at  Taunton  a  dahlia  of  a  rather 


ITS   DANGERS   AND   ITS   DETECTION.  91 

common  variety,  and  such  as  most  gardeners 
would  call  pui-ple,  —  a  dark  pink,  with  a  shade 
of  blue  over  it,  —  and  requested  forty-four  differ- 
ent people  to  write  me  down  what  they  would  call 
its  color.  In  their  replies  I  got  fourteen  different 
names  for  it.  I  sent  a  flower  of  the  same  kind  to 
a  lady,  who  returned  me  twelve  replies  from  mem- 
bers of  her  family  and  friends,  and  in  the  twelve 
were  eight  different  names."  I  would  here  refer 
to  the  very  interesting  chapter  on  the  growth  of 
the  color  vocabulary  in  Mr.  Grant  Allen's  book, 
"The  Color-Sense." 

I  cannot  do  better  than  give  also  the  statements 
of  another  highly-educated  color-blind,  from  whom 
I  have  before  quoted  (Mr.  William  Pole),  who 
says,— 

"  The  color-blind  must  be  very  liable  to  associate,  almost 
indissolubly,  the  true  normal  name  of  a  color  with  the 
sensation  it  conveys  to  their  minds,  whatever  that  sensation 
may  he ;  and  they  may,  therefore,  easily  be  led  to  speak  of 
that  color  as  if  they  saw  it  Hke  other  people,  although  the 
sensation  they  refer  to  may  be  really  of  quite  a  different 
nature  to  that  w^hich  the  name  implies.  A  color-blind  per- 
son will  be  especially  loth  to  believe  that  certain  colors, 
which  he  hears  about  and  talks  about  every  hour  of  the  day, 
can  be  invisible  to  him.  Objects  of  these  hues  will  probably 
present  to  his  mind  some  ideas  of  color  (though  not  the  true 
ones),  and  he  may  naturally  imagine,  therefore,  that  he  does 
see  them,  and  may  give  his  description  accordingly.  And 
this  sort  of  error  is  very  much  enhanced  by  the  fact  that  it 
is  not  an  easy  matter  to  refer  different  tones  of  any  one  color 
to  the  same  color-sensation ;  so  that  a  modification  of  tone, 
if  considerable,  may  be  easily  supposed  to  be  a  different 
color.  I  believe  this  difficulty  is  also  felt  by  the  normal- 
eyed;  and  the  popular  nomenclature  of  colors  furnishes 
illustrations  of  the  fact,  different  tones  of  the  same  color 
having  often  different  names,  and  being  treated  as  separate 


92  COLOR-BLINDNESS  : 

colors.  Pink  and  crimson,  lilac  and  violet,  are  well-acknowl- 
edged examples  of  this ;  and  a  dark  shade  of  orange  is  called 
brown,  which  generally  passes  for  a  separate  color.  Hence 
we  may  easily  see  what  a  great  probability  there  is  that  the 
color-blind  may  acquire  the  habit  of  attaching  the  names  of 
different  colors  to  what  are,  in  reality,  only  varieties  of  the 
same  sensation ;  and  as  this  habit  dates  from  their  infancy, 
and  is  encouraged  by  their  every-day  communication  with 
the  world,  it  is  much  more  difficult  to  get  rid  of  than  might 
be  supposed.  The  sufferer  may  find  himself  continually 
blundering;  but  he  must  go  through  a  very  rigid  self- 
examination  before  he  can  trace  this  to  the  fact  that  some 
of  the  principal  ideas  he  has  all  his  life  held  upon  color 
are  mere  delusions.  Taking  red  as  an  example,  it  is  in  the 
highest  degree  natural  that  persons  who  are  continually 
seeing  this  color  under  the  appearance  of  dark  yellow 
should  imagine  that  the  latter  sensation  (which  is  cer- 
tainly very  distinct  from  that  of  full  yellow)  is  what  cor- 
responds to  the  term  red;  and  the  notion  that  they  cannot 
really  see  red  at  all  is  one  they  have  the  greatest  difficulty 
in  comprehending.  Hence  the  very  general  assertion  by  the 
color-blind  that  they  do  see  red,  —  an  assertion  which  I 
think  has  been  far  more  readily  accepted  than  it  ought 
to  be.  Red  is  a  more  common  color  than  dark  yellow  ;  and 
hence  the  preference,  by  the  color-blind,  of  the  former  name 
for  the  common  sensation.  A  great  variety  of  bodies  are 
known  to  be  red  by  habit  and  association,  and  are  for  this 
reason  often  named  correctly.  My  own  experience  is  very 
decided  on  this  point.  It  is  only  after  long  and  careful 
investigation  I  have  come  to  the  conclusion  that  my  sensa- 
tions of  color  are  limited  to  blue  and  yellow.  But,  before  I 
found  this  out,  —  that  is,  for  nearly  thirty  years  of  my  life, 
—  1  firmly  believed  that  what  I  now  know  to  be  only  differ- 
ences in  tone  of  one  or  the  other  of  these  were  different 
colors ;  and  hence  I  was  in  the  habit  of  talking  of  red,  crim- 
son, scarlet,  green,  brown,  purple,  pink,  orange,  &c.,  —  not,  of 
course,  with  the  confidence  of  the  normal-eyed,  but  still 
with  a  full  belief  that  I  saw  them.  If,  therefore,  at  that 
time,  any  scientific  man  had  examined  me,  I  should  have 
given  him  a  description  of  my  case,  which  I  now,  after  more 
careful  study,  know  would  have  been   entirely  wrong.      I 


ITS   DANGERS   AXD    ITS   DETECTION.  93 

should  have  told  him,  among  other  incorrect  statements, 
that  I  saw  red  objects  of  a  full  tone,  such  as  vermilion, 
soldiers'  coats,  &c.,  perfectly  well;  and  I  could,  if  necessary, 
have  supported  my  assertion  by  naming  correctly  a  great 
variety  of  bodies  having  this  color,  which,  indeed,  I  am  in 
the  habit  of  doing  every  day.  It  would  have  been  inferred, 
with  great  appearance  of  truth,  that  I  was  really  impressible 
with  the  red  sensation  ;  but  I  now  see  what  an  erroneous 
inference  this  would  have  been. 

''  Another  source  of  confusion  in  interpreting  the  descrip- 
tions of  the  color-blind  is  the  want  of  due  appreciation  of 
the  different  sensations  that  may  be  produced  on  their  minds 
by  modified  hues  of  the  same  general  color.  The  normal- 
eyed  person  considers  green,  for  example,  as  always  green, 
whether  it  be  yellow  green,  neutral  green,  or  blue  green. 
Whatever  the  particular  '  shade  of  green,'  as  it  is  called,  it 
still  has,  in  his  eye,  the  distinguishing  character  of  green- 
ness, which  cannot  be  hidden  or  disguised  by  any  predomi- 
nance of  blue  or  yellow  it  may  contain.  But  with  the  color- 
blind this  identifying  characteristic  of  greenness  is  wanting ; 
and  hence  several  patients,  speaking  of  green,  may,  by  each 
having  reference  in  his  own  mind  to  some  different  hue  of 
the  color,  describe  it  in  the  most  contradictory  terms.  One 
may  say,  with  perfect  sincerity,  that  green  appears  to  him 
like  red ;  another,  that  it  looks  yellow ;  a  third,  blue ;  a  fourth, 
black;  a  fifth, orange ;  a  sixth,  violet,  —  from  which  the  nor- 
mal-eyed examiner,  impressed  with  the  unity  of  greenness, 
may  naturally  infer  that  each  person  is  suffering  under  a  dif- 
ferent species  of  the  disorder;  while,  by  proper  interpreta- 
tion, these  anomalous  descriptions  would  only  convey  the 
expression  of  one  consistent  truth,  and  one  perfectly  uni- 
form defect  of  vision." 

This  very  clear  and  admirable  description  of  a 
color-blind's  perception  not  only  shows  us  how  and 
what  they  see,  but  it  also  explains  some  of  the 
ver}^  many  ways  in  which  they  escape  detection. 
If  so  intelligent  a  person  as  Mr.  Pole  could  have 
been  so  long  ignorant  of  his  own  perception,  we 
need  not  wonder  that  the  uneducated  color-blind 


94  COLOR-BLINDNESS  : 

should  not  be  aware  of  their  defect  even  in  adult 
life,  and  still  less  that  their  defect  remains  con- 
cealed. 

Let  us  turn  now  to  Professor  Holmgren's  valu- 
able  remarks  on  this  point.     He  says,  — 

"  We  must  remember  that  color-blindness  is  not  a  disease, 
in  the  sense  of  being  attended  with  suffering,  obliging  the 
individual  to  have  recourse  to  a  physician.  Color-blindness, 
quite  as  well  as  normal  sight,  is  a  sense  of  color,  though  of 
another  and  a  more  simple  nature.  He  whom  we  call  color- 
blind is  not,  correctly  speaking,  at  all  blind  to  colors.  He 
perceives,  in  the  main,  the  same  kind  of  light  as  the  normal 
observer,  but  sees  a  part  of  it  in  another  manner.  In  the 
system  according  to  which  he  arranges  his  colors,  he  has 
fewer  kinds  than  the  normal  observer;  and  this  is  why  he  is 
obliged  to  classify  under  the  same  denomination  a  portion  of 
the  colors  classed  by  the  normal  observer  under  different 
heads.  It  results  from  this  that  he  finds  resemblances  be- 
tween colors,  or  confuses  others,  that  the  normal  observer 
finds  different;  for  instance,  red  and  green.  These  con- 
fusions naturally  surprise  and  amuse  the  normal  observer, 
who  readily  imagines  that  it  arises  from  very  great  ignorance 
of  colors,  or  from  defective  training.  He  ordinarily  sup- 
poses that  there  is  no  limit  to  the  mistakes  the  color-blind 
might  make  in  this  respect.  But  such  is  not  the  case  :  he 
obeys  laws  quite  as  exact  as  does  the  normal  observer.  A 
color-blind  person  can  no  more  accustom  himself  to  seeing 
colors  as  the  normal  observer  does,  than  the  red-blind  can 
see  colors  in  the  same  way  that  the  green-blind  does,  or 
conversely. 

"  This  theory,  v/hich  is  based  upon  experience,  explains 
to  us  how  the  color-blind  see  colors ;  but,  if  we  only  base 
our  ideas  on  the  names  given  to  colors  by  the  color-blind,  we 
can  be  easily  deceived.  To  judge  correctly  of  color-blind- 
ness, and  the  various  practical  questions  connected  with  it,  it 
is  of  the  highest  importance  to  distinctly  observe  the  differ- 
ence between  the  manner  in  which  the  color-blind  person  sees, 
and  the  manner  in  which  he  names,  colors.  The  sensation  is 
based  upon  the  nature  of  the  sense  of  color  in  the  organiza- 
tion of  the  optic  nerve  from  birth.     The  7iame,  on  the  con- 


ITS   DANGERS   AND   ITS   DETECTION.  95 

trary,  is  learned.  It  is  conventional :  it  depends  upon 
exercise  and  habit.  The  names  of  colors  are  naturally  the 
objective  expression  of  subjective  sensations  ;  but,  on  the 
other  hand,  they  are  regulated  by  the  system  of  normal 
sight,  and  cannot,  consequently,  agree  vidth  that  of  the  color- 
blind. They  can,  nevertheless,  be  learned  by  the  latter,  and 
even  applied  correctly  in  many  cases.  There  is  connected 
with  this  fact  a  jDeculiarity  of  the  utmost  importance  prac- 
tically to  the  question  in  point,  and  one  that  has  given  rise 
to  the  most  serious  embarrassments  and  misunderstandings. 
This  has  been  and  is  still  one  of  the  chief  causes  of  our 
erroneous  ideas  on  the  subject  of  color-blindness  existing  in 
the  masses,  because  it  is  the  veil  under  which  this  defect 
usually  conceals  itself  from  our  observation  in  every-day 
life,  and  under  which,  even  to  the  last  moment,  it  will  suc- 
ceed in  escaping  discovery  in  cases  where,  as  frequently 
happens,  the  methods  of  exploration  employed  are  indecisive, 
or  are  based  upon  erroneous  principles. 

"If  we  reflect  on  the  condition  of  the  color-blind,  it  is 
difficult  to  understand  how  he  can  avoid  being  detected  in 
his  daily  intercourse  wdth  men  endowed  with  normal  sight. 
And  yet  experience  has  sufficiently  controverted  this  idea. 
That  which  we  have  acquired  in  examining  en  masse  the 
personnel  of  a  railway,  for  example,  where  it  is  required 
night  and  day  to  give  attention  to  colored  signals,  is  singu- 
larly worthy  of  notice.  AYe  learn  by  it  that  a  number  of 
color-blind  were  discovered,  although  their  defective  sense 
of  color  had  never  been  suspected  by  themselves  or  any  one 
else,  and  the  majority  had  correctly  performed  their  duties." 

Very  few  of  us  who  have  good  color-perception 
are  aware  how  wholly  the  name  of  a  color  becomes 
the  name  of  an  attribute  of  any  special  object,  and 
hence  how  this  name  may  be  misplaced.  It  seems 
hardly  possible  that,  notwithstanding  a  good  color- 
perception,  the  names  of  color  are  so  much  a  matter 
of  learning  and  memory.  As  Professor  Holmgren 
says,  — 

"  This  especially  applies  to  the  color-blind,  who  seek  in 
every  way,  and  without  themselves  being  aware  of  it,  to 


96  COLOE-BLINDNESS  : 

supplement  the  chromatic  sense  nature  has  refused  them. 
As  color  is  an  immutable  quality  of  a  number  of  objects, 
some  of  which  are  of  one,  some  of  another  color,  it  is  not 
very  difficult  to  learn  by  heart  the  names  of  their  colors. 
The  immediate  impression  is  not  necessary  for  this.  We 
may  hear  a  blind  person,  even  one  born  so,  give  the  exact 
names  of  the  colors  of  ordinary  and  well-known  objects  of 
which  he  has  heard.  For  a  color-blind  person  this  is  easier, 
because  he  obtains  some  help  from  his  incomplete  chromatic 
sense." 

To  practically  test  this,  I  thought  of  examining 
some  young  blind  people  before  whom  the  subject 
had  not  been  discussed,  and  who  would  answer  to 
the  best  of  their  knowledge  and  ability.  The  fol- 
lowing table  contains  the  results  obtained  in  seven 
such  cases.  The  last,  the  eighth,  a  boy  of  fifteen, 
was  not  wholly  blind  to  color ;  and  it  will  be  seen 
how  different  his  answers  were.  He  was  prac- 
tically as  blind  as  the  other  seven  as  to  form,  &c. 


1 


ITS   DANGERS   AKD   ITS  DETECTION. 


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ITS  DAKGEES  AND  ITS   DETECTION.  99 

These  seven  young  people  were  pupils  of  the 
Perkins  Institution  for  the  Blind  at  South  Boston, 
who  were  blind  from  birth,  not  only  as  to  form, 
but  also  as  to  color.  The  importance  of  this  point 
will  pcrhai)s  onlj-  be  appreciated  by  the  specialist, 
who  is  aware  that  those  wholly  blind  as  to  form 
may  enjoy  quite  good  color-sense.  The  superin- 
tendent had  informed  me  that  "  there  were  only 
eleven  who  were  blind  from  birth,  and  about  thir- 
teen pupils  who  were  supposed  to  have  lost  their 
sight  before  the  age  of  four  months."  I  found, 
however,  I  had  to  reject  all  but  the  seven  from  my 
list.  The  others  were,  of  course,  practically  blind ; 
but  their  knowledge  of  colors  was  to  a  greater  or 
less  extent  learned  through  the  eye,  and  not  merely 
a  name  for  a  quality.  Their  answers  to  my  ques- 
tions were  very  different,  as  will  be  seen  by  those 
of  one  of  them,  which  I  append  to  my  list.  He 
had  to  look  for  some  time  at  a  briHit-red  book  to 
determine  its  color,  and  voluntarily  said  it  was 
"hard  for  him  to  get  hold  of  colors."  Before  I 
tried  him  with  the  red  book,  I  noticed  his  answers 
were  peculiar ;  and  he  spoke  of  "  shades  of  color." 
I  was  confident  that  the  others  were  totally  blind, 
both  to  color  and  light,  from  examination  of  their 
eyes,  and  by  testing  with  colored  objects,  and  ques- 
tioning as  to  the  position  of  the  large  windows  in 
the  room,  &c.  These  pupils  were  not  aware  of 
what  was  to  be  asked  of  them,  and  those  examined 
not  allowed  to  communicate  with  the  others  w^ait- 
ing.  They  will  naturally  be  useless  for  further 
tests  of  this  character,  as  the  colors  of  objects  will 
be  now  pretty  thoroughl}^  talked  about  in  the  in- 
stitution, and  much  learned  from  intercom  muni  ca- 


100  COLOR-BLINDNESS  : 

tion  as  to  the  "  color-name  "  of  objects,  if  I  may 
use  this  term.  I  doubt  if  any  but  a  specialist,  and 
one  wholly  on  his  guard,  could  have  obtained  just 
this  interesting  series  of  answers.  Difference  in 
intelligence  and  memory  was  marked,  and  largely 
decided  the  answers  given,  as  also  the  way  they 
were  given.  The  examination  was  extremely  in- 
teresting, and  the  pupils  seemed  to  be  rather 
pleased  at  being  put  to  the  test  of  their  knowledge 
and  memory.  The  two  girls  answered  quickly  as 
to  water,  having  lately  heard  a  lecture  about  it. 
As  to  the  sky  and  water,  teaching  had,  of  course,  a 
direct  bearing;  the  very  way  some  replies  were 
given  proving  they  were  learned  by  the  ear,  and 
not  by  the  eye.  Could  the  look  of  the  face  or 
gesture  or  tone  be  added  to  these  answers  here 
simply  written  down  in  short,  much  more  force 
would  be  given  my  argument.  Through  the  ear 
alone  these  answers  were  learned,  and  retained  by 
memory.  The  attachment  of  the  name  of  a  color 
to  an  object  is  an  attribute  not  learned  by  the  eye 
alone.  A  wholly  uneducated  person  who  handles 
bricks,  if  he  hears  them  called  black,  will  so  call 
them  when  questioned  as  to  their  color. 

Dr.  Stilling  says,  as  a  word  of  warning  to  those 
who  are  testing  for  color-blindness,  — 

"It  is  a  well-known  fact  that  color-blind  persons,  by 
exercising  their  faculty  of  judgment,  can  aid  their  want  of 
sensibility,  and  are  able  to  conceal  their  defect  to  a  certain 
extent.  They  have  learned  the  names  of  colors  quite  as 
well  as  normal-sighted  people;  and  by  the  help  of  every 
outward  sign  they  have  acquired  a  certain  knowledge  of 
those  pigments  to  the  characteristic  tints  of  which  they  are 
blind.  Very  often  that  knowledge  is  developed  in  a  surpris- 
ing degree.     Therefore,  in  testing  one  who  is  color-blind,  we 


ITS   DAXGEES   AND  ITS  DETECTION.         101 

must  take  away  the  possibility  of  employing  any  of  those 
outward  characteristics  which  he  is  wont  to  make  use  of 
according  to  long  experience.  This  is  so  much  the  more 
important,  as  most  persons  of  this  description  have  not  the 
least  suspicion  of  their  imperfect  power  of  sight.  Only  very 
intelligent  people  understand  their  defect." 

Professor  Holmgren  very  shrewdly  observes,  — 

"  If  we  watch  the  development,  or  rather  the  education  of 
the  child's  color-perception,  it  will  be  seen  that  they  first 
learn  the  names  of  colors,  and  afterwards  their  correct  use, 
in  defining  characteristic  peculiarities  of  known  objects.  It 
is  much  later  that  they  notice  the  quality  of  the  light  in 
correctly  designating  colored  objects  they  have  not  pre- 
viously seen.  The  child  with  defective  color-perception 
differs  from  the  normal-eyed  only  in  not  being  able  to  reach 
this  degree.  He  learns,  like  the  others,  that  the  sky  is 
blue,  the  grass  green,  bricks  are  red.  He  learns  that  the 
corn  is  green  in  spring  and  yellow  in  autumn ;  that  the  pop- 
pies have  a  green  bud,  but  red  flow^ers,  &c.  :  these  and  many 
other  things  are  retained  in  his  memory.  If  he  thinks  over 
the  meaning  of  these  names,  he  soon  meets  with  difficulties 
which  may  lead  to  very  various  results.  Upon  the  color- 
blind eye  the  brick,  the  tile,  the  barley  in  spring  and  in  the 
fall,  and  the  poppy-flower  produce  the  same  color-sensation, 
and  he  can  with  difficulty  comprehend  why  different  names 
are  given  to  these  colors.  Most  persons  do  not  reflect  so  far, 
and,  regarding  the  problem  as  one  they  cannot  solve,  lose 
therefore  all  interest  in  the  study  of  colors ;  concerning  them- 
selves with  them  only  when  forced  to.  This  readily  explains 
why  the  color-blind  grow  up  without  others  detecting  their 
defective  chromatic  sense.  This  is  generally  the  case  with 
the  lower  classes,  and  especially  in  the  country.  The  ma- 
jority get  into  no  difficulty  from  their  intercourse  with  colors; 
and,  if  they  make  gross  mistakes,  this  is  attributed  to  lack 
of  practice,  or  carelessness.  Hence  nothing  more  is  thought 
of  it. 

"  Other  persons,  however,  reflect  further.  In  seeking  why 
there  are  two  separate  names  for  similar  colors,  as  the  grass 
and  bricks,  they  look  for  some  more  delicate  mark  of  differ- 
ence, and  finally  find  it ;  but  this  is  only  the  varying  degree 


102  COLOR-BLINDNESS  : 

of  the  intensity  of  the  light.  One  color  is,  perhaps,  paler 
than  the  other.  From  the  time  this  is  noticed,  they  become 
very  timid  in  discriminating  colors.  They  accustom  them- 
selves to  find  a  difference  of  color  in  the  difference  of  the 
intensity  of  light,  the  luminosity,  and  lead  others  as  well  as 
themselves  into  the  error  of  supposing  that  they  see  the  ex-- 
ternal  world  like  other  jDCople,  and  that  their  uncertainty  is 
wholly  due  to  want  of  practice.  We  find,  in  fact,  in  the 
color-blind  a  very  practised  and  sharp  eye  for  variations  of 
intensity  of  light.  They  often  have  acute  vision,  and  can 
see  well  at  a  distance.  The  first  color-blind  known  to  sci- 
ence, Harris,  observed  this  of  himself ;  and  it  has  been  sup- 
ported by  nearly  all  observers  since.  There  are,  moreover, 
very  few  color-blind  so  interested  as  Dalton  to  study  their 
own  case,  and  detect  their  fault." 

As  we  have  seen,  Mr.  Pole  is  the  only  one  since 
Dalton's  time  who  has  studied  and  reported  his 
own  chromatic  defect. 

I  have  now  shown  how  the  color-blind  deceive 
themselves  and  others,  and,  growing  up  in  igno- 
rance of  their  defect,  escape  detection.  To  this 
must  be  added  the  very  important  fact,  that,  till 
very  recently,  methods  of  testing  for  color-blind- 
ness have  been  used  which  were  wholly  inade- 
quate to  expose  particularly  the  lighter  forms  of 
the  trouble.  It  must  be  remembered  that  red  or 
green  or  violet  blindness  may  exist  in  any  degree 
from  the  most  complete  to  almost  normal  vision. 
Formerly,  if  a  color-blind  gave  the  right  color- 
names  to  objects,  he  was  regarded  as  normal-eyed ; 
and  tliis  has  been  continued  notwithstanding  the 
repeated  warnings  of  Seebeck,  Helmholtz,  Holm- 
gren, and  others.  Thus  many  have  escaped  detec- 
tion ;  whilst,  on  the  other  hand,  the  normal-eyed's 
ignorance  of  names  has  been  set  down  to  color- 
blindness, giving  us,  as  in  France,  most  extraordi- 
nary percentage. 


ITS  DAKGEES   AND  ITS  DETECTION.         103 

But  we  now  know  that  about  one  male  in  five 
and  twenty  is  color-blind.  It  is  impossible  for  all 
to  have  grown  up  ignorant  of  their  defect.  How, 
therefore,  has  this  class,  who  are  aware  of  their 
color-blindness,  escaped  detection  in  every-day  life? 

The  color-blind,  who  are  quick-witted  enough  to 
discover  earl}^  that  something  is  wrong  with,  their 
vision  by  the  smiles  of  their  listeners  when  they 
mention  this  or  that  object  by  color,  are  equally 
quick-witted  in  avoiding  so  doing.  They  have 
found  that  there  are  names  of  certain  attributes 
they  cannot  comprehend,  and  hence  must  let  alone. 
They  learn,  also,  what  we  forget,  that  so  many 
objects  of  every-day  life  always  have  the  same 
color,  as  red  tiles  or  bricks,  and  the  color-names  of 
these  they  use  with  freedom ;  whilst  they  often, 
even  unconsciously,  are  cautious  not  to  name  the 
color  of  a  new  object  till  they  have  heard  it  ap- 
plied, after  which  it  is  a  mere  matter  of  memory 
stimulated  by  a  consciousness  of  defect.  I  have 
often  recalled  to  the  color-blind  their  own  acts  and 
words,  and  surprised  them  by  an  exposure  of  the 
mental  jugglery  they  employed  to  escape  detec- 
tion, of  which  they  were  almost  unaware,  so  much 
had  it  become  a  matter  of  habit.  Another  impor- 
tant point  is,  that,  as  violet-blindness  is  very  rare, 
the  vast  majority  of  defective  are  red  or  green 
blind.  These  persons  see  violet  and  yellow  as  the 
normal-eyed,  and  they  naturally  apply  these  color- 
names  correctly.  When,  therefore,  they  fail  in  red 
or  green,  a  casual  observer  attributes  it  to  simple 
carelessness,  —  hence  a  very  ready  avoidance  of 
detection.  It  does  not  seem  possible  that  any  one 
who  sees  so  much  correctly,  and  whose  ideas  of 


104  COLOE-BLTNDNESS  : 

color  SO  correspond  with  our  own,  cannot  be 
equally  correct  throughout,  if  they  will  but  take 
the  pains  to  notice  and  learn.  Color-blindness  is 
also  a  constant  source  of  petty  mortification,  which 
teaches  its  possessor  to  be  on  constant  guard  over 
himself  in  avoiding  exposure  and  its  accompany- 
ing irritation.  The  intelligent  color-blind  finds 
many  ways  of  drawing  a  decision  of  color  from 
those  he  is  in  contact  with,  and  always  lets  shop- 
keepers pick  out  the  colors  he  calls  for,  just  as  the 
color-blind  shopkeeper  lets  his  customer  do  the 
same  if  he  can ;  and  when  he  fails  in  this,  and 
makes  mistakes  enough  to  lose  his  place,  he  can 
take  refuge  in  the  mourning  stores,  where  his 
defect  is  an  advantage. 

This  brings  us  again  to  their  extraordinary  ap- 
preciation of  light  and  shade.  They  can  sort  and 
place  in  correct  order  a  series  of  shades  of  red  or 
green  much  better  and  more  quickly  than  the 
normal-eyed,  because  to  them  the  color  is  but  so 
much  light  and  dark.  Now,  an  educated  color- 
blind is  asked  by  a  lady  friend  to  buy  a  skein  of 
red  worsted  to  match  the  pattern.  He  asks  the 
attendant  in  the  store  for  red  worsteds,  and  se- 
lects the  one  which  corresponds  in  luminosity  with 
his  pattern.  Such  good  '-'•  shopping  "  forbids  the 
idea  of  any  chromatic  defect.  But  the  worsted 
attendant  is  away,  and  another,  who  is  color-blind, 
v][uietly  hands  over  the  greens  to  the  purchaser: 
the  latter  will  then  complacently  select  the  one 
which  matches  in  luminosity  his  red  pattern.  If 
he  is  green-blind,  he  will  select  a  lighter  green  — 
if  red-blind,  a  darker  —  than  his  pattern.  In  either 
case  his  defect  is  exposed;  and,  in  fact,  it  thus 
often  happens. 


ITS   DA>s"GERS   AND   ITS   DETECTION.         105 

This  sensitiveness  to  light  and  shade  has  enabled 
color-blind  painters  to  follow  their  profession  with 
success,  and  even  avoid  discovery,  until  accident  or 
design  has  interchanged,  for  instance,  their  reds 
and  greens.  A  color-blind  engraver  has  an  advan- 
tage over  his  fellow-workmen.  It  seems  hardly 
possible  that  a  color-blind  person  should  have  the 
ideas  and  thoughts,  and  power  of  expressing  these, 
which  are  derived  wholly  from  the  perception  of, 
and  acquaintance  with,  colors.  Hence  I  quote  the 
following  as  a  peculiar  instance  of  concealment  of 
color-blindness,  where  it  would  seem  that  it  must 
show  itself.  Of  a  member  of  a  well-known  color- 
blind family,  the  reporter  says,  — 

"  Another  of  the  gentlemen  whose  case  of  defective  per- 
ception of  colors  is  herein  noticed,  is  generally  acknowledged 
as  one  of  the  first  and  greatest  of  American  poets  now  liv- 
ing. He  also  is  unable  to  distinguish  one  tune  from  another; 
yet  his  poetry  is  not  deficient  in  the  requisites  of  perfect  ca- 
dence, harmony,  and  rhythm.  In  regard  to  color,  his  defect 
is  such  as  is  described  in  the  '  worst  degree '  of  the  arrange- 
ment of  Dr.  Hays.  He  says,  that,  previous  to  the  time  at 
which  he  ascertained  this  peculiarity  of  vision,  he  always 
wondered  that  people  should  talk  of  '  glorious  sunsets  '  and 
'beautiful  sunsets,'  inasmuch  as  he  could  detect  neither 
'  glory '  nor  '  beauty  '  in  them.  The  kaleidoscope  of  nature 
and  the  harmonicon  of  art  are  the  Utopias  of  his  mind. 
The  magic  hues  developed  by  the  prism,  the  iridescence  of 
shells  and  minerals,  the  inimitable  colors  of  the  beasts  and 
birds  of  tropical  climates,  tlie  verdure  of  the  fields  of  spring, 
the  splendor  of  the  autumnal  foliage  of  the  forests,  the 
myriad  hues  of  flowers,  and  the  realm  of  beauty  which 
springs,  as  sprang  Minerva  from  the  brain  of  Jupiter,  from 
the  genius  of  the  artist,  —  all  these,  it  would  appear,  are, 
comparatively,  '  as  a  sealed  book  '  to  him.  Yet  from  his  icrit- 
inrjs  no  evidence  of  this  can  he  detected.  The  poet  throws  his 
gossamer  veil  of  ideality  before  the  vision  of  the  7nan,  con- 
verting a  sombre  world  into  a  paradise  like  that  of  the  Per- 


106  COLOR-BLINDNESS  : 

Bian.  Seated  on  the  borders  of  Helicon,  lie  looks  abroad 
upon  a  universe  transformed  by  imagination  and  glowing 
with  all  the  colors  of  a  phantasmagoria.  The  iris  of  heaven 
lifts  its  expansive  arch  in  hues  as  varied  and  as  vivid  as 
when  first  placed  there  '  to  establish  a  covenant '  between 
God  and  manf  the  sun  descends,  now  invested  wdth  the 
mellow  tints  of  the  skies  of  Italy,  and  now  surrounded  by 
clouds  emblazoned  like  those  which  attend  its  setting  in 
America  alone ;  fields  are  clad  with  a  carpet  of  emerald, 
and  flowers  blossom  with  all  the  diversity  of  coloring  that 
ever  decked  them  in  the  gardens  of  the  East ;  birds  spread 
to  the  wind  pinions  as  gorgeous  as  those  that  wave  over  the 
Amazon  or  the  Ganges  ;  and  the  mineral  world  glitters  with 
the  concentrated  beauty  of  amethyst,  topaz,  beryl,  and  all 
the  precious  stones  adorning  the  foundations  of  the  wall 
of  the  New  Jerusalem  which  was  revealed  unto  the  apostle 
at  Patmos." 

As  the  color  of  most  of  our  common  berries  and 
fruits,  when  ripe,  is  the  complementary  of  that  of 
the  green  foliage,  the  inability  to  see  and  collect 
them  is  a  very  frequent  source  of  the  exposure  of 
the  color-blind  both '  to  themselves  and  their  sur- 
roundings in  early  life.  It  is  therefore  a  wonder 
how  a  person  can  grow  up,  and  not  be  found  out, 
much  less  not  find  themselves  out. 

Professor  Wilson,  in  his  book,  says  of  a  chemist 
aged  twenty-eight,  green-blind,  — 

"  He  worked  five  months  in  my  laboratory;  and  some 
time  elapsed  before  I  discovered  his  color-blindness,  w^hich 
he  was  not  ready  to  acknowledge,  and  could  to  a  great  ex- 
tent conceal  by  his  sagacity  in  observing  those  properties 
of  bodies  wliich  are  not  affected  by  color.  He  unconsciously 
betrayed  an  effort  to  supplement  his  defective  vision  of 
colors  by  all  secondary  aids.  If  colored  papers  were  shown 
him,  he  fixed  upon  any  difference  in  shape,  smoothness,  or 
configuration  which  they  presented,  and,  when  they  were 
shown  him  again,  recognized  them  by  differences  which 
would  have  escaped  most  other  eyes.     He  would  frequently, 


ITS   DANGERS    AND   ITS   DETECTION.  107 

accordingly,  have  appeared  to  a  stranger  to  recognize  colors, 
when  in  reality  he  was  only  recalling  form,  or  condition  of 
surface,  of  the  colored  body." 

I  was  lately  called  upon  to  test  some  employes 
in  a  large  printing-house,  and  found  two,  among 
the  seventeen  presented  to  me,  color-blind.  The 
astonishment  of  their  fellow-workmen  was  very 
great ;  and  they  would  not  believe  one  of  the  men 
could  be  defective,  since  his  emploj^ment  was  cut- 
ting up  colored  cardboard  and  paper.  They  car- 
ried him  to  his  post,  and  asked  him  to  pick  out 
the  colors,  which  he  did,  as  they  were  always  kept 
in  certain  positiojis  on  the  shelves.  The  members 
of  the  firm,  however,  were  convinced  by  the  ex- 
amination, and  quickly  realized  the  risk  of  loss  of 
material  and  time  from  the  man's  defect,  hitherto 
unsuspected. 

An  interesting  instance  of  what  constant  prac- 
tice will  do  in  helping  a  color-blind  to  avoid  mis- 
take and  detection  is  given  by  Dr.  Minder,  who 
says,  — 

"  On  this  point  (of  possible  alleviation  or  cure)  a  descrij)- 
tion  of  three  cases  of  color-blindness  in  a  Jewish  family  of 
Berne  will  be  of  value.  They  are  brothers,  the  youngest 
already  over  fifty  years  of  age.  They  are  all  feebly  red- 
blind,  and  happen  to  be  in  business  which  requires  daily 
intercourse  with  colors.  They  all  make  the  same  mistakes 
when  tested  with  the  worked-w^orsted  tables.  I  could  un- 
fortunately only  persuade  one  to  be  more  thoroughly  tested. 
To  my  surprise  I  only  detected  him  by  Holmgren's  test 
after  repeated  trials,  and  that  by  his  matching  bright-blue 
a-nd  rose  color.  He  is  a  very  intelligent  gentleman,  wdiose 
business  has  required  him  for  more  than  thirty  years  to  be 
daily  busied  with  colors,  with  which,  according  to  his  own 
and  his  wife's  report,  he  formerly  made  constant  mistakes. 
These  have,  in  the  course  of  years,  occurred  less  and  less 


108  COLOE-BLINDNESS  : 

frequently.  He  was  even  very  highly  valued  for  his  fine 
appreciation  of  colors,  and  taste  in  their  selection,  by  a  Paris 
ribbon-factory  with  which  he  was  connected.  He  attends 
alone  to  all  the  buying  for  his  large  business,  and  is  only 
liable  to  mistake  with  dark  green  and  black,  rose  and  light 
blue.  According  to  his  statement,  he  could  not,  in  early 
years,  be  certain  of  violet  and  green.  I  was  perfectly 
astonished  at  his  power  of  distinguishing  the  various  colors, 
and  the  number  of  names  he  had  at  disposal  for  the  finest 
shades.  I  was  equally  surprised  at  his  so  accurate  compari- 
son of  the  several  colors  with  each  other.  To  this  he 
attributed  his  so  greatly  cultivated  color-perception.  He 
laughed,  therefore,  at  Holmgren's  method  of  comparison, 
by  which  he  was,  he  thought,  not  to  be  caught ;  and,  in  fact, 
this  could  only  be  done  with  difficulty.  The  results  of 
other  methods  were  negative,  except  with  the  polariscope, 
where  he  always  stopped  at  rose  and  bright  blue,  which,  he 
declared,  were  alike,  and  sometimes  called  them  both  rose, 
and  sometimes  bright  blue." 

This  case  led  Dr.  Minder  —  as  it  would  also 
likely  lead  others  —  to  suppose  that  there  was  a 
basis  for  Dr.  Favre's  belief  in  the  curability  of 
color-blindness  by  exercise  and  practice  with  col- 
ors ;  but  no  one  can  have  tested  and  talked  with 
many  color-blind  without  being  convinced  that  we 
can  hardly  set  any  limit  to  their  capacity  for  learn- 
ing other  attributes  of  colored  objects,  and  recog- 
nizing and  remembering  their  color-names  through 
this  alone.  Thus,  as  we  now  well  know,  they 
may  even  deceive  themselves,  as  well  as  others, 
into  the  belief  that  they  have  gained  by  practice 
a  color-perception  they  were  not  born  with.  This 
we  shall  see  in  Professor  Delboeuf's  supposed  cor- 
rection of  color-blindness  by  looking  through  cer- 
tain transparent  media. 

A  brother-practitioner,  who  is  color-blind,  and 
whom  I  was  testing  by  Holmgren's  method,  after 


ITS   DANGERS    AND   ITS    DETECTION.  109 

sitting  some  time  with  the  one  hundred  and  fifty 
little  skeins  of  worsted  before  him,  finally  said,  "  I 
have  tried  so  hard  to  supplement  my  defect  by 
every  possible  means,  and  catch  other  attributes 
than  color  to  recall  the  names  of  them,  that,  if  you 
will  give  me  two  or  three  days  to  study  over  these 
worsteds,  and  tell  me  what  their  colors  are,  I  will 
afterwards  pick  them  all  out  correctly;  but  I  shall 
see  them  no  differently." 

My  friend.  Dr.  Henry  Power,  writes  me  from 
London,  June  1,  1878, — 

"  Color-blindness  is  a  subject  of  great  public  concern. 
As  showing  also  its  private  relation,  I  may  mention  an 
interesting  case  that  came  under  my  care  lately,  in  which 
the  man  was  a  draper,  who  had  long,  by  great  ingenuity, 
conducted  a  business  on  his  own  account;  always  getting 
an  assistant  to  bring  down  the  particular  bundle  of  color 
demanded  by  the  customer,  and  then  selecting  the  particu- 
lar tint  by  its  shade.  He  was  now  going  into  a  much  larger 
business,  and  wanted  to  know  if  his  disease  could  be  cured, 
or  whether  his  future  partners  should  be  told  of  his  defect. 
A  "no  "  and  a  "  yes  "  settled  these  points,  and  I  have  heard 
no  more  of  him;  but  it  was  curious,  that,  in  the  course  of 
twenty-five  years,  he  had  never  been  found  out." 

I  was  recently  told  of  the  following :  Some  five 
and  twenty  years  ago,  before  color-blindness  was 
so  well  known  or  talked  of,  a  student  of  the  Royal 
Academy  in  London  —  who  was  selected,  not  only 
by  the  authorities,  but  also  by  his  fellow-students, 
as  having  about  the  best  perception  for  form,  and 
power  of  light  and  shade  —  turned  to  the  use  of 
colors.  In  this  it  was  naturally  supposed  he  would 
exhibit  extraordinary  talent,  and  become  a  great 
painter.  He  was  allowed  to  take  a  portrait  by 
Titian  from  the  National  Gallery,  and  have  it  in  a 
imall  room  to  himself.     There  he  copied  it  to  his 


110  COLOR-BLINDNESS  : 

best  ability,  as  he  stated  to  the  principal  and  his 
brother-students.  No  one  had  seen  hun  at  work. 
His  result  was  the  most  perfect  copy  as  far  as 
light  and  shade  went,  but  in  pea-green.  He  finally 
became  an  engraver. 

0 


ITS  DANGEES  AND   ITS   DETECTION.  Ill 


CHAPTER  XII. 

INCURABrLITY  OF  CONGENITAL  COLOE-BLINDNESS. 

The  question  of  the  curability  of  congenital 
color-blindness  is  one  of  considerable  importance ; 
for  certainly  the  color-blind  railroad  employe  or 
pilot  should  not  be  dismissed  from  service  if  he 
jcan  be  cured  of  his  defect. 

It  has  been  till  lately  universally  admitted  by 
ophthalmic  surgeons  and  physiologists  that  con- 
genital color-blindness  was  incurable  by  any  known 
means.  In  August,  1874,  Dr.  A.  Favre  of  Lyons, 
France,  reported  to  the  French  Congress  for  the 
Advancement  of  Science,  at  Lille,  some  observa- 
tions, which  seemed  to  him  to  prove  that  congenital 
color-blindness  was  curable  both  in  children  and 
adults  by  exercising  the  chromatic  sense.  Dr. 
Favre  has  for  the  last  twenty  years  or  more,  as 
consulting  surgeon  of  the  Paris,  Lyons,  and  Mediter- 
ranean Railroad  Company,  pressed  the  necessity 
of  examining  all  railroad  employes  for  color-blind- 
ness, led  so  to  do  principally  by  the  results  of 
Wilson  and  Potton.  He  has  succeeded  in  indu- 
cing other  roads  to  adopt  similar  precautions,  and 
deserves   great   credit    for   his    exertions.     It   is 


112  COLOR-BLINDNESS  : 

therefore  due  him  to  look  carefully  at  his  state- 
ments, as,  if  correct,  they  are  of  the  utmost  im- 
portance. 

He  reports  the  results  in  eleven  different  schools 
of  the  examination  of  1,002  boys  between  the 
ages  of  four  and  fifteen.  These  their  teachers 
tested  by  asking  them  to  name  the  color  of  objects 
exhibited  of  five  principal  colors.  The  teachers 
reported  to  Dr.  Favre  that  they  found  at  least 
218  defective  in  chromatic  sense,  and  that  almost 
all  were  perfectly  cured  by  being  repeatedly  shown 
objects,  and  told  the  names  of  their  colors  till  they 
were  learned.  Amongst  138  girls,  from  seven  to 
fourteen  years  of  age.  Dr.  Favre  himself  found 
only  2  whom  he  regarded  as  color-blind.  These 
girls,  he  remarks,  were  under  excellent  teachers, 
and  a  large  number  had  passed  through  the  salles 
d'asile^  where  colors  were  taught.  Dr.  Favre  then 
says,  — 

"  The  examination  of  these  several  reports  shows  that 
many  children  of  both  sexes  come  into  the  salles  d'asile  and 
schools  without  a  notion  of  the  elementary  colors.  The 
number  of  children  lacking  in  this  sensation  in  the  majority 
of  boys'  schools  I  have  visited  is  from  twenty  to  thirty  per 
cent.  This  ratio  diminishes  in  proportion  as  the  attention 
of  the  scholars  is  directed  by  their  teachers  to  colored  ob- 
jects. Certain  exercises,  the  painting  of  plans,  geographical 
cards,  lessons  in  natural  history,  &c.,  have  an  evident  influ- 
ence on  the  scholars'  i)rogress  in  this  sense.  Amongst  the 
girls,  sewing-work,  embroidery,  the  care  of  the  clothing, 
the  handling  of  flowers,  much  reduces  at  eight  years  of  age  the 
number  of  those  who  have  difiiculty  in  distinguishing  one  or 
more  of  the  elementary  colors.  At  this  age  the  number  of 
boys  who  make  marked  mistakes  in  naming  colors  is  still 
quite  large ;  and  we  have  found,  that,  if  the  majority  easily 
acquire  a  knowledge  of  colors,  many  of  these  need  watchful 
and  continued  care,  requiring  to  be  examined  periodically, 


ITS   DAXGERS    AND   ITS   DETECTION^.  113 

BO  to  speak,  till  we  are  assured  of  their  cure.  What  is  the 
best  method  to  use  in  the  schools  ?  Experience  may  teach 
us  further ;  but,  from  our  observations  during  the  last  five 
years,  we  feel  authorized  to  draw  the  following  conclusions : 
Male  and  female  teachers  should  be  required —  (1)  To  ques- 
tion separately  the  scholars  of  their  class  as  to  the  five  ele- 
mentary colors,  and  also  as  to  white  and  black.  (2)  To 
carefully  record,  at  the  time  of  examination,  the  scholar's 
replies  against  his  name.  (3)  The  scholars  who  have 
made  mistakes  should  be  individually  called  twice  a  week, 
and  the  colors  named  before  them ;  they  should  be  ques- 
tioned and  taught  till  it  is  shown  that  they  have  acquired  an 
exact  notion  of  the  elementary  colors.  (4)  There  should 
be  periodic  examinations.  (5)  Whenever  occasion  pre- 
sents, the  precise  names  of  colored  objects  exhibited  should 
be  spoken  before  the  whole  class.  (6)  An  advanced  course 
on  colors  should  be  given  scholars  destined  for  special  pro- 
fessions, by  the  aid  of  Chevreul's  color-chart  and  the  most 
commonly  manufactured  articles. 

"  The  treatment  of  color-blindness  in  the  adult  also  has 
given  us  very  conclusive  results,  which  we  have  embraced 
in  an  unpublished  article  presented  to  the  Academy  of  Sci- 
ence." 

Dr.  Favre  says  again  elsewhere,  — 

"  I  call  for  the  introduction  of  exercises  with  colors  in  all 
the  schools,  in  the  army,  in  the  marine,  and  on  the  railroads. 
I  am  persuaded,  that,  by  the  precautions  I  have  indicated,  a 
great  number  of  accidents  may  be  avoided ;  and  I  hope  to 
be  so  fortunate  as  to  cause  congenital  Daltonism  to  be 
stricken  from  the  nosological  list." 

Dr.  Favre  has  here  undoubtedly  simply  mistaken 
the  lack  of  knowledge  of  the  name  of  a  color  for 
a  lack  of  jjerception  of  the  color.  In  this  mistake 
he  has  been  confirmed  by  the  rather  extraor- 
dinary reports  from  his  several  friends  who  were 
teachers.  These  latter,  I  must  at  once  insist,  were 
wholly  incompetent  to  decide  whether  their  schol- 
ars were    color-blind.     We   must   of  course   first 


114  COLOR-BLINDNESS  : 

positively  prove  the  existence  of  the  defect  before 
we  can  talk  about  having  cured  it.  It  is  next  to 
impossible  for  even  an  expert  to  decide  whether  a 
child  is  color-blind  by  simply  asking  him  to  name 
the  color  of  pieces  of  paper  or  other  objects.  It 
is,  on  the  other  hand,  very  possible  to  teach  him 
a  name  which  he  shall  attach  to  the  object,  as  it 
would  also  be  to  teach  a  congenital  blind  person. 
These  children,  supposed  color-blind,  are  reported 
as  cured  by  more  or  less  exercise  with  colors, 
according  to  their  individual  quickness  and  mem- 
ory in  catching  and  retaining  their  names.  Those 
that  were  dull,  inattentive,  and  forgetful,  required 
repeated  exercises  before  they  retained  the  names 
of  colors  which  were  seemingly  readily  forgotten. 
This  is  perfectly  shown  by  the  teachers'  reports. 

The  reported  percentage  of  defective  color-per- 
ception found  would  of  itself  throw  much  doubt 
on  the  method  of  testing.  For  instance,  as  many 
as  thirty  out  of  fifty,  and  fifteen  out  of  thirty-five, 
children  are  reported  having  "  no  notion  of  color." 
But  ten  per  cent  is  a  very  large  ratio,  even  when 
we  include  all  cases  of  only  slight  color-blindness. 
Now,  these  children  were  from  four  to  fifteen  years 
of  age.  How  many  schoolboys  at  this  time  of  life 
know  the  names  of  five  colors,  or,  having  heard 
them,  will  apply  them  correctly  when  questioned, 
without  being  specially  taught  ? 

We  have  found  it  very  different  with  girls,  as 
did  Dr.  Favre.  They  use  the  names  of  colors 
much  more  frequently,  and  have  more  to  do  with 
colored  objects  in  dress,  trimmings,  &c. 

Those  of  us  who  possess  normal  color-perception 
know  how   difficult  it  is   to   tell   the   difference 


ITS   DANGERS    AND   ITS   DETECTION.  115 

between  light  greens  and  blues.  This  formed  a 
large  class  among  these  supposed  defective  chil- 
dren, and  they  were  reported  cured  in  four  or  five 
exercises.  A  further  convincing  proof  of  the 
inadequacy  of  the  test  employed,  and  of  the  dis- 
qualification of  the  teachers  as  examiners,  is  shown 
by  their  reporting  children  as  confounding  those 
colors  which  the  color-blind  never  do ;  for  exam- 
ple, red  and  violet.  I  would  not,  of  course,  deny 
that  amongst  these  thousand  children  there  were 
any  color-blind.  Proof  to  the  contrary  exists  in 
the  statement  of  one  teacher,  who  says,  "  I  some- 
times despaired  of  curing  one  child,  six  and  a  half 
years  old,  who,  after  sixty-five  exercises,  could  not 
tell  me  a  single  color  without  hesitation.  Eleven 
exercises  more,  however,  cured  tliis  unexampled 
Daltonian,  who  began  by  first  distinguishing  green, 
and  finished  by  not  always  calling  red  yellow 
when  shown  him."  This  child,  no  doubt,  was  color- 
blind, and  took  this  length  of  time  to  learn  the 
name  of  a  color  to  be  repeated  whenever  the  same 
object  ivas  shoiun  him.  If  alive,  I  am  certain  this 
boy  is  as  color-blind  now  as  then;  and  any  test 
not  calling  for  the  use  of  names  would  undoubt- 
edly prove  it.  Professor  Helmholtz,  in  his  "  Phys- 
iological Optics"  Cp.  299,  1867),  said,— 

"  As  to  the  examination  of  the  color-blind,  simply  asking 
them  to  name  this  or  that  color,  will  naturally  elicit  but  very 
little,  since  they  are  then  forced  to  apply  the  system  of 
names  adapted  to  normal  perception  to  their  own  percep- 
tion, for  which  it  is  not  adapted.  It  is  not  only  not  adapted, 
because  it  contains  too  many  names,  but,  in  the  series  of 
spectral  colors,  ice  designate  differences  of  tone  as  such,  which 
to  the  color-blind  are  only  variations  of  saturation  or  lumi- 
nosity. It  is  more  than  doubtful  whether  what  they  call 
yellow  and  blue  correspond  to  our  yellow  and  blue." 


116  COLOR-BLINDNESS  : 

At  first  sight  it  seems  only  natural  that  we 
should  be  able  to  improve  our  color-perception  by 
use,  as  we  may  sharpen  our  other  senses  by  exer- 
cise;  but  in  the  color-blind  there  is  a  congenital 
defect  or  deficiency.  With  the  ear  we  may  learn 
to  distinguish  sounds  whose  vibrations  come  within 
the  range  of  our  scale ;  but  no  amount  of  instruc- 
tion can  make  us  hear  a  note  above  or  below  the 
vibratory  scale  of  our  ear.  A  little  practice  will 
enable  the  normal  eye  to  discriminate  between  the 
lighter  shades  of  green  and  blue,  which  at  first  it 
had  confounded ;  but  no  amount  of  exercise  with 
colors  can  cause  the  color-blind  eye  to  perceive 
those  colors  as  we  do,  to  whose  ethereal  wave 
lengths  or  numbers  it  is  not  adapted.  However 
much  practice  may  cultivate  the  power  of  an 
organ,  it  can  never  give  that  organ  a  different  or 
additional  power.  I  admit  that  constant  exercise 
may  enable  a  person  only  partially  color-blind  to 
improve  his  capacity  for  discriminating  colors  ;  but 
even  then  I  do  not  believe  he  has  altered  his  color- 
perception,  but  only  supplemented  it  by  additional 
means,  as  we  so  often  see  other  senses,  when  defi- 
cient, supplemented.  Whether  we  shall  ever  be 
able  to  cure  color-blindness  is  another  question  I 
am  not  in  position  to  decide.  I  desire  here  only 
to  state  my  belief,  shared  in  at  present  by  all 
physiologists  and  ophthalmic  surgeons,  that  it  has 
not  been  and  cannot  be  cured  by  exercise  with 
colors.  From  Dr.  Favre's  valuable  researches,  and 
his  well-known  and  recognized  connection  with 
the  present  great  advance  in  the  testing  for  color- 
blindness amongst  railroad  employes  and  else- 
where, his  belief  in  the  curability  of  this  defect 


ITS   DANGERS   AND   ITS   DETECTION.  117 

might  have  undue  weight.  It  must  be  remem- 
bered that  he  stands  ahnost  alone  in  this.  I  have 
therefore  endeavored  to  show  how  and  why  he 
was  mistaken,  as  others  also  might  well  be.  To 
this  opinion  I  must  still  hold,  notwithstanding  Dr. 
Favre's  more  recent  article  before  the  Lyons  Medi- 
cal Society,  and  the  supposed  cases  of  congenital 
color-blindness  he  there  describes. 

I  should,  perhaps,  not  dwell  on  this  point  further, 
were  it  not  that  Dr.  Favre's  mistake  might  lead  to 
dangerous  consequences  by  quieting  the  fears  of 
those  whose  attention  had  been  roused  to  the  ne 
cessity  of  testing  for  color-blindness.  I  therefore 
quote  from  one  or  two  authorities  in  support  of  my 
opinion,  to  show  that  not  only  is  it  incurable, 
so  far  as  we  3'et  know,  but  that  it  does  not  change 
with  time.  A  congenital  color-blind  person  dies 
so.     Professor  Wilson  says,  — 

"  Congenital  color-blindness  is  certainly  incurable,  and, 
when  induced  by  injury  or  disease,  it  may  become  as  irreme- 
diable as  if  it  had  been  an  inherited  peculiarity;  but  certain 
forms  of  this  affection  from  disease  or  injury  are  transitory, 
and  admit  of  cure.  So  far  as  I  can  ascertain,  from  the  ex- 
amination of  the  cases  of  congenital  color-blindness  within 
my  reach,  the  amount  of  modification  in  the  perception  of 
colors,  induced  by  age,  is  inappreciable,  even  though  no 
allowance  be  made  for  that  alteration  in  all  the  powers  of 
vision  which  time  produces  on  every  eye.  Thus  Dalton 
was  certainly  as  color-blind  at  the  Oxford  meeting  of  the 
British  Association  in  1832,  when  he  compared  the  color 
of  his  D.C.L.  gown  to  that  of  the  leaves  of  trees,  as  in 
1792,  when  he  first  discovered  his  color-blindness ;  nor  did 
any  change,  so  far  as  his  associates  were  aware,  occur  in  his 
perceptions  of  color  up  to  his  death  in  1844.  Mr.  Milne,  of 
Edinburgh,  is  still  (October,  1854)  as  color-blind  as  he 
was  when  Mr.  Combe  described  his  case  thirty  years  ago, 
and  as  he  had  been  for  years  before  his  case  was  described. 


118  COLOR-BLINDNESS  : 

Professor  N.  was  examined  as  to  his  perception  of  color, 
some  thirty  years  since,  by  Sir  David  Brewster,  who  has 
recorded  his  case.  He  writes  me  recently,  '  I  am  under 
the  impression  that  some  change  in  appreciating  colors  took 
place  in  my  eye  between  childhood  and  youth.  As  a  child, 
red  gooseberries  seemed  to  me  altogether  blue,  so  far  as  I 
remember.  Latterly  I  have  observed  what  I  fancy  red  in 
this  variety  of  fruit.'  And  again:  'I  suppose  sometimes 
that  I  can  distinguish  red  in  some  objects  ;  but  probably  this 
is  from  knowing  that  they  are  usually  of  this  color. '  But 
he  adds,  '  At  any  rate,  I  am  quite  sure  I  should  make  a 
dangerous  railway-signal  man,  as  I  most  certainly  would 
not  know  a  red  flag  from  a  green  one.'  This  gentleman 
further  states,  in  answer  to  some  queries,  that  pink  still 
appears  to  him  by  daylight  Uue,  and  by  gaslight  green,  and 
that  he  continues  to  confound  carmine  red  by  daylight  with 
blue.  There  plainly  has  been  nothing  deserving  the  name 
of  improvement  in  his  case.  Lastly,  the  Countess  of  D. 
has  not  (in  1853)  appreciably  altered  in  her  color-blindness 
since  her  peculiarities  were  described  by  Wollaston  many 
years  ago. 

"Dr.  K.,  a  medical  man,  says,  'When  a  boy  at  school, 
my  attention  was  directed  to  my  want  of  knowledge  of  color 
by  finding  I  could  not  see  what  my  father  called  the  brighl- 
red  berries  of  the  holly.  When  other  children  easily  found 
out  the  trees  which  were  loaded  with  ripe  cherries,  I  never 
could,  till  I  came  so  near  the  tree  as  to  detect  the  form  of 
the  fruit.  The  discovery  of  this  defect  in  vision  distressed 
my  father  exceedingly ;  and  he  endeavored  to  cultivate  in  me 
a  knowledge  of  color  by  giving  me  lessons  in  painting, 
making  colored  charts  for  me  of  the  prismatic  and  other 
colors,  wishing  to  believe  that  the  defect  resulted  from  want 
of  education  in  color,  not  from  a  visual  defect.  I  destroj^ed 
many  a  painting  of  flowers,  &c.,  by  putting  on  wrong  colors, 
—  as  blues  for  purples,  green  for  some  kinds  of  red,  and 
yellow  for  others.  I  still  remember  the  surprise  he  exhibited 
when  he  found  I  could  not  detect  a  red  cloak  spread  over  a 
hedge  across  a  narrow  field.  Hedge  and  cloak  appeared  to 
me  the  same  exact  hue,  and  they  do  so  to  this  day.' 

"  Dr.  T.,  aged  twenty-seven,  early  became  aware  of  his 
inability  to  distinguish  colors,  and  has  cultivated  paint- 


ITS   DANGERS   AND   ITS   DETECTION.  119 

Ing  in  the  hope  of  curing  or  diminishing  his  defect,  but 
without  any  success.  He  has  himself  favored  me  with  an 
account  of  his  case  ;  but,  as  he  very  strongly  realizes  the 
want  of  a  common  language  between  himself  and  those  who 
have  not  his  defect  in  distinguishing  colors,  he  regards  this 
account  as  hopelessly  imperfect. 

"It  is  quite  certain  that  dyers,  painters,  weavers,  clothiers, 
and  the  members  of  other  callings  much  conversant  with 
color,  are  not  unfrequently  color-blind.  I  myself  have  very 
recently  been  oif ered  any  '  reasonable  fee  '  if  I  would  cure  a 
worthy  working  tailor  of  almost  total  inability  to  distinguish 
colors. 

"  These  cases  may  suffice  to  illustrate  the  permanency  of 
this  affection  of  vision  ;  but  they  are  not  singular.  Among 
my  color-blind  acquaintances  there  are  probably  none  who 
would  not  sacrifice  a  great  deal  to  see  perfectly,  and  nearly 
all  have  endeavored  to  cure  themselves  of  their  visual 
idiosyncrasy ;  but  not  one  reports  a  cure,  and  the  best  edu- 
cated and  most  observant  among  them  are  the  most  decided 
in  declaring  that  they  have  given  up  all  hopes  of  amend- 
ment. 

"  It  is  difficult  to  convince  many  that  this  conclusion  is  a 
just  one.  Those  whose  own  sense  of  color  is  delicate,  and 
who  are  led  by  taste  or  profession  to  live  much  among  colored 
objects,  are  slow  to  believe  that  any  eye  can  be  so  peculiar 
in  its  endowments  as  to  make  the  blunders  which  the  color- 
blind do,  even  in  reference  to  what  they  call  a  '  staring  '  red 
or  green.  Such  colorists  insist  that  carelessness,  indifference, 
or  improper  education  lies  at  the  bottom  of  the  mistakes 
which  the  '  supposed '  color-blind  make,  and  profess  them- 
selves willing  to  undertake  their  cure,  of  wliich,  however, 
they  record  no  case. 

"  When  we  find  an  engraver,  who  for  the  greater  pai-t  of 
his  life  has  been  gazing  all  day  at  paintings,  purchasing  a 
red  window-curtain  for  a  green  one ;  a  tailor,  whose  eye  has 
been  for  hours  daily  fixed  on  cloths  of  very  varied  colors^ 
matching  green  tape  with  scarlet  linen,  at  the  risk  of  losing 
his  situation ;  an  experienced  field-geologist  compelled,  when 
surveying  a  red-sandstone  district,  to  take  a  companion  with 
him  to  point  out  where  grass  ends  and  sandstone  begins ; 
and  a  teacher  of  chemistry  evading  as  much  as  possible 


120  COLOR-BLINDNESS  : 

the  questions  of  his  pupils  concerning  the  colors  of  bodies, 
—  we  cannot  doubt,  that,  after  education  has  done  all  that 
it  can  towards  developing  the  sense  of  color  in  the  color- 
blind, they  remain  as  helplessly  prone  to  make  their  charac- 
teristic blunders  as  before.  A  crowning  example  of  this  has 
recently  presented  itself  to  me.  In  the  establishment  of  a 
painter  and  glass-stainer,  who  is  an  obstinate  disbeliever  in 
the  existence  of  color-blindness,  my  attention  was  recently 
directed  by  his  fellow-workmen  to  a  youth  who  had  been 
set  to  repaint  the  devices  on  the  shafts  of  a  sheaf  of  arrows. 
These  devices,  consisting  of  alternate  circles  of  red  and  green, 
had  not  been  effaced,  but  only  dulled ;  yet  the  painter  exe- 
cuted his  task  by  painting  all  the  red  rings  green,  and  all 
the  green  rings  red.  The  case  was  remarkable  for  the  direct 
reversal  of  the  colors  in  question,  and  this  by  one  who  held 
them  before  him  to  compare,  both  on  his  palette  and  on  the 
arrows.  Yet  the  party  who  committed  the  mistake  was  an 
excellent  draughtsman,  much  esteemed  by  his  master,  and 
surrounded  at  his  daily  work  with  splendid  specimens  of 
stained  glass.  This  mistake  which  he  made  soon  ceased  to 
be  a  solitary  one  :  for  his  fellow-workmen,  having,  since  its 
occurrence,  put  him  to  the  test,  found  him  uncertain  in  his 
judgment  of  many  colors ;  and,  on  examining  him,  I  found 
him  commit  the  characteristic  errors  of  the  color-blind. 
Here,  then,  was  the  possessor  of  an  educated  color-blind  eye 
making  such  mistakes  as  no  normal- eyed  person,  however 
uneducated  his  power  of  vision  might  be,  could  or  would 
make.  Education,  then,  can  do  nothing  towards  curing 
congenital  color-blindness ;  nor,  in  truth,  can  any  thing  else." 

Dr.  Goubert,  in  1867,  says,  as  to  treatment  of 
color-blindness,  — 

"  I  have  here  no  more  consoling  words  or  fruitful  resources 
to  present.  Whatever  the  symptoms  characterizing  this 
peculiar  imperfection,  it  belongs  to  that  large  number  which 
the  divine  art  of  ^sculapius  is  powerless  to  cure,  perhaps 
even  to  mitigate.  All  ophthalmic  surgeons  are  unanimous 
on  this  point." 

Professor  Holmgren  has  very  thoroughly  dis- 
cussed   Dr.    Favre's   publications;   and   he   is  in 


ITS   DANGERS   AlTD   ITS   DETECTION.  121 

position,  both  theoreticall}^  and  practically,  to  test 
attempts  to  cure  color-blindness  by  exercise  with 
colors,  &c.  After  citing  from  his  pamphlets,  he 
says,  — 

"We,  on  our  part,  have  not  yet  seen  the  result  of  a  sys- 
tematic exercise  in  learning  colors  pursued  months  or  years  ; 
but  the  obsei-vations  we  have  made  on  the  exercise  of  the 
color-blind  and  their  general  effects  may  not  be  without 
interest,  and  throw  some  light  on  the  importance  of  such 
exercise.  We  have  said  that  the  color-blind  railroad  em- 
ployes learn  to  distinguish  the  flag-signals  in  common  use, 
and  rarely  make  a  mistake  when  examined,  especially  on  this 
point.  Does  this  result  depend  on  the  training,  and  in  what 
way  ?  The  color-blind  who  are  not  railroad  employes  can 
answer  this.  If  we  show  them  the  ordinary  flags  (green  and 
red),  one  after  the  other,  they  will  nearly  always  name  one 
or  the  other  wrongly,  and  often  both,  and  even  sometimes 
frankly  admit  they  do  not  know  the  true  names  of  the  colors. 
But  if  we  show  them  the  two  flags  at  the  same  time,  and  ask 
which  is  green  and  which  red,  they  at  once  see  a  difference ; 
and,  having  fixed  the  name  in  their  memory,  they  no  longer 
make  mistakes,  but  will  tell  the  true  name  of  the  colors,  even 
when  sho^Ti  one  flag  after  the  other.  From  this  we  see  how 
the  color-blind  railroad  employe  has  learned  to  distinguish 
the  flags. 

"  But,  after  all,  what  have  they  learned?  and  what,  strictly 
speaking,  have  they  gained  by  such  recognitions  ?  If  we  ask 
a  color-blind  person  who  is  intelligent  and  honest,  and  who 
has  no  interest  in  concealing  his  fault,  he  will  openly 
admit  that  he  has  no  idea  of  the  color  itself,  but  that  he 
notices  a  sensible  difference  in  that  the  green  flag  is  darker 
to  his  eye  than  the  red.  At  the  next  trial  he  will  make  the 
same  mistake  if  the  first  flag  is  shown  him  alone,  and  will 
be  as  surely  correct  if  the  two  are  shown  together.  A  rail- 
road employe  who  daily  sees  the  two  flags  will  not  in  general 
make  this  mistake  when  the  test  is  repeated :  we  readily 
understand  why.  The  color-blind  has  learned  to  apply  the 
names,  guiding  himself  by  the  difference  in  the  intensity  of 
the  light ;  but  he  still  continues  destitute  of  any  idea  of  color. 
He  is  always  color-blind,  and  has  simply  learned  an  artifice." 


122  COLOE-BLINDNESS  : 

"  Dr.  Favre's  plan  of  gradual  exercising  depends,  of 
course,  on  the  same  idea  ;  only  that  he  uses  several  shades 
of  the  same  color.  Hence  the  intensity  of  the  light  is  not 
necessarily  the  distinguishing  mark.  The  fact  that  in  his 
proposed  exercises  the  objects  are  looked  at  close  to,  assists 
in  no  small  degree  their  being  distinguished ;  for,  close  to, 
there  are  other  attributes  besides  color  and  intensity  of  light 
observable,  whilst  the  flags  are  always  at  a  much  greater 
distance.  The  coloring  material  of  the  different  wools  may 
present  peculiarities,  which  we  do  not  generally  notice, 
because  the  color  itself  is  enough  for  us,  but  which  are  of 
great  assistance  to  the  color-blind.  What  these  differences 
are  is  not  readily  determined.  The  wools,  for  instance,  may 
be  smooth,  rough,  soft,  or  shining,  —  all  qualities  appealing 
to  the  eye. 

"  The  history  of  science  tells  us  of  cases  of  persons  com- 
pletely blind  who  could  easily  and  correctly  distinguish  wool 
of  different  colors  by  means  of  other  senses,  —  smell,  taste, 
or  touch.  The  power  of  touch  in  this  case  deserves  especial 
attention,  as  it  is  of  importance  in  distinguishing  the  pecu- 
liarities of  the  wools  above  mentioned.  The  close  connec- 
tion between  touch  and  sight  in  determining  whether  an 
object  is  smooth,  rough,  &c.,  is  well  known.  The  assistance 
which  these  two  senses  render  each  other  in  a  general  appre- 
ciation of  every  material  surface  is  not  less  well  known. 
These  are  the  very  qualities,  beyond  any  doubt,  that  the 
color-blind  call  to  their  aid  to  supply  the  place  of  their  de- 
fective color-sense.  Therefore  many  color-blind  place  the 
samx^les  of  wool  in  different  lights,  bring  them  quite  close  to 
the  eye  and  in  different  angles  to  the  visual  axis.  But 
many  color-blind,  who  knew  the  difference  between  red  and 
green,  or  purple  and  green,  frankly  acknowledged  that  they 
only  recognized  them  because  one  wool  was  coarser,  harsher, 
or  rougher  than  the  other.  Consequently  it  was  not  the 
color,  —  that  is,  the  quality  of  the  reflected  light,  —  but  the 
coloring  matter  and  its  peculiar  effects  upon  the  wool,  which 
v\^ere  to  them  the  distinguishing  features.  The  color-blind 
may,  however,  be  assisted  by  still  other  more  accidental 
peculiarities ;  for  instance,  they  may  notice  whether  one 
bunch  of  worsted  is  larger  or  thicker  than  the  other.  The 
results  of  such  exercise  will  be  as  useless  as  a  lesson  simply 


ITS   DANGERS   AND   ITS   DETECTION.  123 

learned  by  heart.  The  scholar  may  repeat  a  "whole  page  of 
his  book  word  for  word,  and  yet  have  no  idea  of  the  mean- 
ing of  the  contents." 

As  to  the  necessity  and  value  of  teaching  the 
names  of  colors  in  the  schools,  I  entirely  agree 
with  Dr.  Favre.  No  better  proof  of  it  can  be 
given  than  the  reports  of  his  teacher-friends,  whd 
found  twenty  to  thirty  per  cent  of  their  pupils 
who  did  not  know  the  names  of  colors,  or  could 
not  apply  them.  Such  recreations  as  color-teach- 
ing would  be  interesting  and  valuable,  since  most 
probably  all  marked  cases  of  color-blindness  would 
be  detected,  and  a  scholar  thus  be  warned  in  time 
not  to  attempt  work  in  after-life  for  which  his 
defect  unfits  him,  of  which  he  cannot  be  cured  by 
any  now  known  means. 

Something  in  the  way  of  teaching  the  names  of 
colors  has  been  already  commenced  in  our  Boston 
schools.  I  have  shown  those  interested  how  neces- 
sary some  instruction  is  in  colors,  as  also  how 
useless  it  would  be  to  attempt  to  correct  color- 
blindness by  teaching  names,  which  would  only  be 
associated  with  objects,  and  not  placed  as  the  ex- 
pression of  an  attribute  recognized  by  the  eye. 
But  the  teachers  must  first  be  taught  what  color- 
blindness is,  and  how  frequent  it  is,  in  order  not  to 
set  down  as  stupid,  or  punish,  an  unfortunate  boy, 
who  seemingly  ivill  not  learn  colors  he  cannot  see. 

As  to  the  possible  mitigation  or  cure  of  color- 
blindness, my  own  experience  with  educated  color- 
blind adults  has  been  very  interesting.  All  had 
attempted,  in  one  way  or  another,  to  overcome 
their  defect  by  practice,  but  in  vain.  Those  who 
best  understood  their  trouble  most  realized  this, 


124  COLOPt-BLINDNESS  : 

and  eagerly  asked  for  relief,  which  can  be  but  par- 
tially obtained. 

I  think  the  necessity  of  discussing,  as  far  as  I 
have,  what  at  first  sight  seemed  perhaps  only  a 
medical  opinion,  has  now  been  made  apparent. 
The  very  mistake  Dr.  Favre  has  been  led  into 
has  also  deceived  railroad  officials,  who  here  and 
there  have  tested  an  employe,  suspected  of  color- 
blindness, with  the  flags  or  lanterns  used  on  their 
individual  roads.  It  requires  considerable  argu- 
ment and  positive  proof  to  convince  a  railroad 
superintendent  that  one  of  his  men,  whom  he  has 
had  cause  to  suspect,  and  has  seemingly  thoroughly 
tested,  is,  after  all,  color-blind.  It  is  very  difficult 
for  him  not  to  believe  his  employe  has  learned,  or 
can  be  made  to  learn,  to  see  colors  as  they  appear 
to  a  normal  eye.  He,  however,  will  be  con- 
vinced against  his  reason,  when  the  color-blind 
man  is  in  his  presence  subjected  to  a  proper  scien- 
tific test,  applied  by  a  competent  specialist. 


ITS   DANGERS   AND   ITS   DETECTION.  125 


CHAPTER  XIII. 

PALLIATION   OF    CONGENITAL   COLOR-BLINDNESS. 

As  congenital  color-blindness  cannot  be  cured 
by  any  at  present  known  means,  the  question  of 
its  possible  palliation  becomes  somewhat  impor- 
tant. Many  methods  have  naturally  been  sug- 
gested and  tried,  and  of  these  I  will  now  speak. 
Wilson  says,  — 

"A  means  of  guarding  against  mistakes,  relative  to 
colors,  which  is  unquestionably  of  some  service  to  the  color- 
blind, is  the  reference  of  doubtful  hues  to  a  chromatic 
scale,  accurately  tinted  and  named.  But  this  means  of  cor- 
recting error  soon  finds  its  limit,  as  the  mismatchings  of  red 
with  green,  olive  with  brown,  and  purple  with  blue,  charac- 
teristically made  by  the  color-blind  (although  both  colors 
are  presented  to  the  eye  together),  are  sufficient  to  show. 
Moreover,  we  must  remember,  that,  to  the  color-blind,  his 
defective  color  perfectly  corresponds  with  gray,  or  white 
and  black,  as  readily  shown  by  experiment  with  Chevreul's 
^  qammes  chromatlques,'  or  with  the  worsted  test.  Hence,  by 
comparison  alone,  he  might  decide  that  his  scarlet  or  green 
cloth  is  a  neutral  tint  or  gray." 

Szokalski  and  Seebeck,  as  "Wilson  also  remarks, 
recommended,  as  a  means  of  ameliorating  the  con- 
dition of  the  color-blind,  their  steady  gazing,  first 
on  a  colored  surface,  and  then  on  a  white  or  black 


126  COLOE-BLTNDNESS  : 

one ;  but,  for  reasons  already  given,  this  proposal 
seems  of  no  value,  nor  is  any  proof  offered  that  it 
has  been  of  service. 

There  nevertheless  exists,  says  Wartman,  a 
very  easy  means  of  rectifying,  to  a  certain  extent, 
the  error  of  the  appellation  of  color.  This  means 
consists  in  examining  colored  objects  through  a 
transparent  medium  —  as  a  glass  or  a  liquid  —  of 
a  certain  known  tint.  Suppose  this  tint  red :  the 
impression  of  a  green  body  and  of  a  red  body,  the 
same  at  first  to  the  naked  eye,  will  become  mani- 
festly distinguished  by  the  use  of  the  transparent 
screen.  This  method  appears  to  have  been  prac- 
tised for  the  first  time  by  Professor  Seebeck  (the 
father)  towards  the  year  1817.  Their  employment, 
however,  only  remedies  mistakes  in  the  sj)ecific 
nature  of  colors,  and  leaves  in  general  those  which 
apply  to  one  and  the  same  tint.  Wilson  says  that 
Dr.  Steebach  carried  out  this  proposal  the  length 
of  recommending  the  use  of  colored  spectacles. 
Trinchinetti  advises  that  the  glasses  should  be  of 
the  color  which  is  the  complement  of  that  liable 
to  be  seen  falsely.  To  this  Wartman  justly 
objects,  because  "the  color-blind  do  not  judge 
correctly  of  complementary  colors ; "  but  his  own 
proposal  to  employ  transparent  media  of  other 
colors  is  liable  to  as  great  objections.  Wilson 
adds,  — 

"  I  am  far  from  wishing  to  affirm  that  a  color-blind  per- 
son may  not  be  aided  in  correcting  his  chromatic  errors  by 
such  a  use  of  colored  glasses  as  Seebeck  and  Wartman 
recommend ;  but,  after  many  trials  with  my  color-blind 
acquaintances,  I  have  found  none  who  could  turn  the  sug- 
gestion to  practical  account.  My  trials  have  been  chiefly 
made   upon   those  who  confused  red  with  green,  to  whom 


ITS   DAXGEES   AND  ITS   DETECTION.  127 

Wartman,   in  illustrating   the  use  of  colored  transparent 
media,  specially  refers  ;  but  I  have  met  with  no  success." 

In  1855  Mr.  J.  Clerk  Maxwell  suggested  and 
tried  the  employment  of  red  and  green  glass  sim- 
ultaneously, which  frees  it  from  Wilson's  objec- 
tions. He  says,  as  to  the  effect  of  colored  glasses 
on  the  color-blind,  — 

"  Although  they  cannot  distinguish  reds  and  greens  from 
varieties  of  gray,  the  transparency  of  red  and  green  glasses 
for  those  kinds  of  light  is  very  different.  Hence,  after  find- 
ing a  case  in  which  red  and  green  appear  identical,  on  look- 
ing through  a  red  glass  they  see  the  red  clearly  and  the 
green  obscurely,  while  tlrrough.a  green  glass  the  red  appears 
dark,  and  the  green  light.  By  furnishing  Mr.  X.  with  a  red 
and  a  green  glass,  which  he  could  distinguish  only  by  their 
shape,  I  enabled  him  to  make  judgments  in  previously 
doubtful  cases  of  color  with  perfect  certainty.  I  have  since 
had  a  pair  of  spectacles  constructed,  with  one  glass  red  and 
the  other  green.  These  Mr.  X.  intends  to  use  for  a  length 
of  time,  and  he  hopes  to  acquire  the  habit  of  discriminating 
red  from  green  tints  by  their  different  effects  on  his  two 
eyes.  Though  he  can  never  acquire  our  sensation  of  red,  he 
may  then  discern  for  himself  what  things  are  red ;  and  the 
mental  process  may  become  so  familiar  to  him  as  to  act  wn- 
consciously  like  a  new  sense." 

It  is  very  generally  remarked  of  and  by  the 
color-blind,  that  they  can  distinguish  reds  and 
greens  better  by  artificial  light  than  in  daylight. 
Many  a  one  has  avoided  detection  by  carrying  ob- 
jects, especially  goods,  to  the  gas  to  enable  them 
to  determine.  The  simple  reason  of  tliis  is  that 
they  can  see,  as  the  normal-eyed,  blue,  and  its  com- 
plement yellow.  The  artificial  light  adds  the  yel- 
low, and  increases  the  yellow  in  the  object  itself, 
thereby  assisting  tlieir  vision.  In  lesser  degrees 
of    color-bUndness    this    result    is    very   marked. 


128  COLOR-BLINDNESS  : 

Wilson  found  that  the  whiter  and  more  intensely 
luminous  artificial  lights,  such  as  the  lime-ball  and 
the  electric  charcoal-light,  induce  the  same  confu- 
sion in  the  perception  of  colors  as  sunlight  does. 
He  says,  — 

"  The  contrast  in  appearance  under  the  opposite  illumina- 
tions is  so  great,  that,  among  the  cases  of  color-blindness 
which  I  have  recorded,  there  are  as  many  as  six  persons  who 
have  discovered  that  they  could  mitigate  then-  peculiarity 
of  vision  by  the  employment  of  artificial  light.  Thus  Mr. 
N.,  Professor  Y.,  and  Dr.  E.  have  resorted  to  candle-light 
as  a  means  of  increasing  their  enjoyment  of  flowers,  which, 
if  crimson,  appeared,  when  seen  by  it,  much  richer  in  color 
than  by  daylight.  Dr.  E.  and  I  had  admired  flowers  to- 
gether for  years  without  my  discovering  his  color-blindness. 
Mr.  N.  states  that  '  it  is  quite  an  enjoyment '  to  him  to  look 
at  crimson  flowers  by  candle-light.  Professor  Y.  has  al- 
ways delighted  in  going  into  a  conservatory  by  candle-light, 
because  then  all  the  purple  and  red  flowers  stood  out  in  such 
brilliant  contrast  to  the  green  leaves.  A  gentleman  who 
deals  in  colored  goods  has  long  been  in  the  habit  of  appeal- 
ing to  a  gas-flame  in  a  dark  room  to  decide  between  scarlet 
and  green,  and  crimson  and  blue." 

Hence  Wilson  proposed  for  the  color-blind  such 
colored  glasses  as  rendered  sunlight  nearest  to 
artificial  light.  These  are  pale  yellow  or  orange, 
stained  with  oxide  of  silver.  Such  glasses  were 
supplied  to  the  above-mentioned  gentlemen.  There 
were  four  shades  or  depths  of  the  yellow  color. 
One  reported,  "The  glasses  deepen,  or  rather 
brighten,  the  reds,  but  do  not  affect  the  greens  so 
much.  I  can  distinguish  the  reds  by  the  aid  of  the 
glasses  much  better  than  I  can  the  greens.  On  a 
bright  day  they  gave  a  decided  and  very  marked 
difference  between  red  and  green.  Scarlets  it  made 
very  bright  and  light ;  while  crimsons  were  made 


ITS   DAGGERS   AND   ITS   DETECTION.  129 

decidedly  red  and  fiery."  Another  found  lie  could, 
through  the  yellow  glass,  see  the  same  difference 
between  green  and  scarlet,  and  crimson  and  blue, 
as  by  artificial  light.  The  color-blind,  therefore, 
can  assist  themselves  and  avoid  mistakes  by  select- 
ing and  looking  through  such  yellow  glass  as  ren- 
ders daylight  nearest  to  artificial  light. 

An  interesting  notice  of  a  red-blind  having  dis- 
covered his  ability  to  see  better  by  lamp-light  is 
given  by  Dr.  Minder.  The  person  was  a  member 
of  the  Bernese  family,  whose  color-blindness,  from 
documentary  evidence,  has  been  known  to  exist 
two  hundred  years.  In  a  letter  dated  Paris,  1799, 
to  his  color-blind  brother,  he  says,  — 

"  You  %TiIl  find  enclosed  a  pretty  Swiss  cockade.  I  have 
separated  it,  but  you  can  readily  put  it  together.  In  the 
centre  is  the  yellow,  then  red,  then  green.  Formerly,  if  I 
had  been  torn  on  the  rack  to  get  this  arrangement  from  me, 
it  would  have  been  useless.  About  a  year  ago,  however,  I 
made  the  brilliant  discovery,  that  by  lamp-light  I  could  dis- 
tinguish the  colors.  Rose-red,  which  by  daylight  is  blue  to 
me,  then  appears  a  bright  carmine ;  green,  which  by  day  is 
red,  appears  blue  :  so  that,  give  me  twenty-four  hours,  I 
should  seldom  be  deceived.  Write  me  if  you  have  ever 
made  this  discovery." 

In  March,  1878,  Professors  J.  Delboeuf  and  W. 
Spring  of  Lille  published  a  very  interesting  and 
important  article  on  the  amelioration  of  color- 
blindness by  looking  tlirough  certain  colored  solu- 
tions. Professor  Delboeuf  is  color-blind ;  and  hence 
his  observations,  guided  by  Professor  Spring  who  is 
normal-eyed,  are  of  such  value,  that  I  will  give  here 
quotations  from  the  original  article.  Delboeuf  s 
theory  as  to  color-perception,  deduced  from  his 
results,  is  not  of  course  in  place  here.     I  would 


130  COLOR-BLINDNESS  : 

only  mention  that  he  endeavors  to  disprove  the 
Young-Helmholtz  theory. 

After  various  trials  with  one  and  another  colored 
fluid,  he  hit  upon  "  fuchsine  "  five  parts  in  weight 
to  fifty  thousai^d  d'eau  alcoolisee.  This  he  placed 
in  a  wedge-shaped  glass  receptacle,  with  sides 
meeting  at  one  end,  and  separated  at  the  other  a 
centimetre.  Thus  he  could  look  through  any 
thickness  up  to  a  centimetre.  He  employed  other 
strengths,  but  the  above  gave  the  best  results. 
Of  these  results  he  says,  — 

"  The  effect  obtained  was  marvellous :  not  only  did  the 
colors  which  I  usually  confound  —  blue,  carmine,  and  violet 
on  the  one  hand,  and  scarlet,  red,  and  brown  on  the  other  — 
appear  very  different,  but  the  scarlet  red  especially  assumed 
a  brightness  wholly  unknown  to  me  heretofore.  It  had  ap- 
peared to  me  dull,  but  suddenly  it  became  flaming  and 
brilliant.  This  was  to  me  an  extraordinary  and  unlooked- 
for  result.  The  same  effect  was  produced  on  two  of  my 
pupils  who  were  color-blind,  and  on  those  whom  Professor 
Spring  and  I  have  examined." 

Professor  Delboeuf  found,  in  brief,  that  the 
fuchsine  corrected  the  usual  mistakes  as  to  red 
fruits  and  flowers,  the  foliage,  &c.  With  Pro- 
fessor Spring  he  also  tested  himself  with  large 
numbers  of  pieces  of  colored  silk. 

■'  Two  of  the  ribbons  were  of  special  service,  —  a  marked 
brown,  which  I  had  confounded  with  a  bright  scarlet  red; 
the  other,  a  violet,  which  produced  on  me  precisely  the  same 
effect  as  a  pure  blue.  The  fuchsine  showed  me  the  differ- 
ence between  the  colors  and  their  shades  with  more  or  less 
distinctness,  and  we  found  the  same  with  the  two  color- 
blind we  tested. 

"  I  had  here,  then,  a  positive  fact,  and  reason  to  suppose 
that  the  fuchsine  rendered  my  vision  like  the  normal-eyed. 
But  this  v.as  a  presumption  I  had  to  verify  by  producing 
color-blindness  in  the  normal-eyed  by  some  solution  before 


ITS   DANGEES   AXD   ITS   DETECTION.  131 

their  eyes.  The  hazard  which  brought  us  the  fuchsine  did 
the  same  for  chloride  of  nickel  one  part,  and  twenty-five  of 
water.  Through  a  centimetre  of  this  solution  Professor 
Spring  found  the  violet  ribbon  looked  blue,  red  identical 
with  brown,  and  nature  assumed  a  certain  uniform  tint 
Mdthout  brilliancy.  Glass  stained  with  copper  has  also 
largely  this  effect  of  rendering  the  normal-eyed  color-blind. 
Holmgren  called  attention  to  this,  and  says,  '  AVe  may  get 
a  good  idea  of  the  difficulty  the  color-blind  have  in  sorting 
colored  objects  if  one  tries  to  do  the  same  through  greenish- 
blue  spectacles.  We  shall  see  and  sort  the  colors  pretty 
much  as  a  red-blind  does,  and  have  the  same  difficulty  as  he, 
or  all  who  attempt  to  do  that  which  they  have  not  the 
power  to.'  I  have  said  that  the  fuchsine  gave  me  a  very 
marked  difference  between  blue  and  violet,  brown  and 
scarlet,  and  that  the  violet  and  scarlet  became  always  more 
brilliant,  whilst  brown  and  blue  retained  their  ordinary 
aspect.  Chloride  of  nickel  does  not  affect  the  normal-eyed, 
except  as  to  red  or  violet ;  green,  blue,  yellow,  remain,  so  to 
speak,  unaltered.  The  reverse  holds  true  wdth  us  ;  namely, 
considerable  thickness  of  the  green  solution  but  slightly 
interferes  with  the  harmony  of  colors  as  I  see  them:  and, 
through  weak  solutions  of  fuchsine,  the  normal-eyed  do  not 
see  objects  very  differently  from  generally.  Stronger  solu- 
tions only  render  the  violet  brighter,  and  especially  the  scar- 
let, which  becomes  whiter. 

"  We  need  now  only  see  if  the  fuchsine  re-establishes  the 
vision  of  a  normal-eyed  rendered  color-blind  by  chloride  of 
nickel.  This  is  the  case.  When  a  normal-eyed  looks  at 
our  silks  through  a  solution  of  chloride  of  nickel  sufficiently 
strong  to  render  the  red  and  brown  ribbons,  the  violet  and 
blue,  appear  either  brown  or  blue,  and  then  adds  a  proper 
thickness  of  fuchsine,  the  colors  regain  their  distinctive 
characters.  So,  also,  a  color-blind  corrected  by  fuchsine 
becomes  again  color-blind  by  chloride  of  nickel." 

Professor  Delboeuf  remarks,  in  closing  his  pa- 
per, — 

"These  researches  have  an  epilogue.  Having  deter- 
mined the  cause  [as  explained  by  his  theory]  of  color- 
blindness, we  should  not  have  thought  of  broaching  the 


132  COLOR-BLINDNESS  : 

question  of  its  treatment,  had  not  a  singular  circumstance 
caused  us  to  believe  in  the  possibility  of  its  cure.  I  have  a 
painting  of  flowers,  —  a  bouquet  of  poppies.  What  alone 
always  pleased  me  in  it  was  the  correctness  of  design,  the 
freshness  of  the  flowers,  and  their  true  and  natural  appear- 
ance. Returning  in  October,  after  an  absence  of  six  or 
seven  weeks,  I  found  a  new  charm  in  this  painting.  I  first 
thought  this  was,  as  is  so  often  the  case  with  works  of  art, 
but  a  momentary  caprice.  Yet  finding  it  each  day  more 
and  more  attractive,  I  thought  whether,  by  looking  through 
the  fuchsine,  and  thus  giving  myself  the  sensation  of  red,  1 
could  not  now  see  distinctions  which  in  reality  were  hitherto 
powerless  to  act  on  my  visual  faculty.  This  conjecture  is 
the  more  plausible  as,  at  the  commencement  of  our  experi- 
ments, I  had  looked  at  this  picture  with  our  apparatus. 
This  was  my  thought  when,  in  the  beginning  of  November, 
I  made  some  tests  of  the  railroad-signals,  to  see  if  our 
liquids  were  sufficient  to  render  distinguishable  the  red  and 
green  lights.  The  results  were  not  conclusive.  I  had  a 
vague  sensation  that  my  naked  eye  could  recognize  distinc- 
tions formerly  impossible  for  me.  But  towards  the  middle 
of  last  December,  whilst  walking  in  the  city,  I  noticed,  or 
thought  I  did,  red  lights  a  few  hundred  steps  off.  I  ap- 
proached them,  and  found  they  were  dim  lanterns  to  mark 
an  excavation  in  the  street.  It  was  the  first  time  that  any 
such  light  seemed  to  have  a  distinctive  color.  Formerly  I 
saw  no  difference  between  the  yellow  and  red  lights,  except 
that  the  former  were  brighter,  and  the  fuchsine  had  but 
made  them  look  alike.  Much  interested,  I  went  over  to  the 
American  tramway,  where  the  cars  are  lighted  by  red  lan- 
terns. I  used  to  notice  but  little  distinction  between  them 
and  the  gas-jets ;  but  to  my  surprise  I  recognized  them  quite 
well,  even  at  a  distance.  I  thought  I  had  perhaps  corrected 
my  color-blindness.  Some  days  after,  when  the  weather 
was  dull,  I  took  out  the  box  of  ribbons  in  my  laboratory. 
Formerly,  on  such  a  day,  I  should  have  unquestionably  found 
them  identical  in  pairs  ;  but  it  was  no  longer  so.  The  brown 
ribbon  remained  the  same ;  but  the  scarlet  struck  me  vividly 
by  its  brightness.  In  no  possible  position  could  I  confound 
them,  and  the  difference  remains  still  quite  marked.  I 
asked  Professor  Spring  to  attempt  to  deceive  me  by  showing 


ITS    DANGERS    AND    ITS   DETECTION.  133 

them  to  me  singly ;  but  he  could  not.  This  I  could  not  say 
of  the  blue  and  violet.  I  thought  I  noticed  a  certain  vari- 
ance, but  did  not  feel  assured  of  not  being  deceived.  I  have 
therefore  to  improve  in  this  direction  ;  but,  no  doubt,  my  in- 
experience with  the  blue  and  violet  is  due  to  my  sensation 
of  red  not  being  yet  very  strong.  In  fact,  the  fuchsine 
gives  the  red  of  my  ribbon  a  color  much  stronger  than  I 
have  as  yet  recognized.  It  is  probably  a  matter  of  time 
and  exercise.  Some  time  after,  I  thought  to  ascertain  if  the 
solar  spectrum  looked  different  from  what  it  formerly  did. 
Going  to  my  laboratory,  and  taking  up  the  ribbons,  I  found 
the  red  brighter  than  the  brown  ;  yet  it  seemed  as  if  the 
contrast  had  somewhat  decreased  lately.  I  looked,  there- 
fore, very  carefully  at  the  spectrum.  I  thought,  at  first,  the 
gradations  more  marked  in  the  yellow,  and  hence,  on  the 
w^hole,  that  there  was  no  change.  Accidentally,  however, 
turning  my  eyes  to  the  ribbons,  I  still  saw  one  was  more 
brilliant,  and,  on  going  to  it,  found  it  was  the  brown  !  It 
was  only  after  a  time,  and  repeatedly  gazing  through  the 
fuchsine,  that  the  red  again  assumed  in  part  its  relative 
brilliancy." 

The  following  very  misleading  notice,  based 
upon  the  above,  I  quote  from  "  The  Scientific 
American,"  Dec.  28,  1878  (p.  408)  :  — 

"  Remedy  for  Color-Blindness.  — '  La  France  Medi- 
cal e  '  states  that  M.  Delboeuf  has  found,  that,  if  a  person 
afflicted  with  Daltonism  looks  through  a  layer  of  fuchsine 
in  solution,  his  infirmity  disappears.  A  practical  applica- 
tion of  this  discovery  has  been  made  by  M.  Javal,  by  inter- 
posing between  two  glasses  a  thin  layer  of  gelatine  previously 
tinted  with  fuchsine.  By  regarding  objects  through  such  a 
medium,  all  the  difficulties  of  color-blindness  are  said  to  be 
corrected." 

More  important  still  is  a  report  from  a  commit- 
tee of  the  Belgian  Royal  Academy  to  the  minister 
of  public  works  in  answer  to  certain  questions. 
Professor  Delboeuf  was  secretary  of  this  commit- 
tee ;  and,  owing  to  his  supposed  discovery  of  tlie 
effect  of  a  fuchsine  solution,  they  report,  — 


134  COLOK-BLINDNESS  : 

"  In  all  cases  there  can  be  attached  to  the  engine  an  ap- 
paratus which  prevents  even  the  most  color-blind  from  pos- 
sibly confounding  red  or  green  with  any  color,  and  which 
would  add  to  the  contrast  of  tho  signals.  The  apparatus 
would  consist  of  a  red  and  a  green  glass  having  the  proper- 
ties spoken  of.  When  the  engineer  had  the  slightest  doubt, 
he  need  but  look  through  these  glasses.  Looking  through 
the  red,  the  signal  of  that  color  would  become  brighter,  and 
contrast  more  with  the  general  visual  field.  On  the  other 
hand,  it  would  be  weakened  by  looking  through  the  green. 
The  reverse  holds  true  of  the  green  signal.  This  apparatus, 
infallible  for  the  day-signals,  would  be  efficacious  to  a  cer- 
tain degree  for  the  night-signals  also,  but  perhaps  less  prac- 
tical here." 

On  this  point  Dr.  Magnus  says,  — 

"  Whether  the  method,  lately  proposed  by  Professor  Del- 
boeuf ,  of  palliating  or  improving  color-blindness  by  f  uchsine- 
colored  glasses,  will  prove  of  service,  time  must  decide.  Pro- 
fessor Delboeuf,  himself  color-blind,  believes  the  method  of 
practical  value,  as  tested  in  his  own  case.  But,  as  we  have 
already  pointed  out,  deception  here  is  very  possible ;  and  one 
may  readily  mistake  for  a  cure  of  color-blindness  the  practice 
which  a  color-blind  has  gained  by  any  increased  sensitive- 
ness to  shades  of  light  in  distinguishing  colors.  Moreover, 
there  has  as  yet  been  no  practical  experience  with  Delboeuf 's 
method." 

In  order  to  fairly  test  Professor  Delboeuf  s  sup- 
posed remedy  or  cure  of  color-blindness,  I  have 
had  the  apparatus  made  as  he  directs  in  his  origi- 
nal article.  With  the  fuchsine  solution  I  have 
pretty  carefully  tested  six  color-blind,  both  red 
and  green  blind,  and  of  various  degrees.  Two  of 
these  were  physicians,  who  had  not  only  paid  a 
good  deal  of  attention  to  the  subject,  but  also  to 
their  own  cases.  The  result  was  quite  unsatisfac- 
tory. A  red-blind,  after  carefully  working  with  the 
fuchsine  solution,  reported  that  he  could  obtain 


ITS   DAXGEES   AND   ITS   DETECTION.  135 

but  little  more  benefit  than  he  did  by  gaslight,  or 
a  pale,  lemon-colored  glass,  which  simulated  gas- 
light. He,  as  they  all,  reported  that  the  green 
worsteds  in  Holmgren's  test,  or  other  objects  of 
this  color,  were  darkened,  and  thereby  the  relation 
of  light  and  shade  altered.  This  assisted  him  in 
selecting  them.  The  same  darkening  takes  place, 
of  course,  with  the  normal  eye.  We  can  see  what 
a  change  in  light  and  shade  is  produced  by  even  a 
small  amount  of  fuchsine,  and  thus  understand 
how  much  the  color-blind  may  hereby  gain  ;  that 
is,  how  much  is  added  to  their  alreadj^  tiigbly  de- 
veloped sense  of  light  and  shade  perception.  A 
color-blind  person  who  had  not  studied  his  defect, 
or  the  subject  generally,  might  very  readily  mis- 
take the  help  of  the  fuchsine  solution  for  a  change 
of  his  color-sense,  and  suppose,  also,  that  the  com- 
parative new  world  to  him  was  something  perma- 
nent, —  this  also  more  especially  as  the  fuchsine 
solution  intensifies  the  reds,  and  allows  a  red-blind 
to  get  a  much  better  idea  of  the  sensation  red  to 
the  normal  eye.  Tliis  is  probably,  therefore,  the 
explanation  of  Professor  Delboeuf's  enthusiasm 
over  his  discovery.  But  those  who  have  studied 
the  vision  of  the  color-blind  —  particularly  the 
educated  —  can  readily  understand  the  fictitious 
assistance  of  a  change  of  light  and  shade,  which, 
as  I  have  said,  one  of  my  color-blind  soon  found 
out. 

Professor  Holmgren,  some  years  before  Del- 
boeuf's investigations,  discussed  the  effect  of  col- 
ored glass  and  colored  solutions  in  rendering  the 
vision  of  the  normal-eyed  like  that  of  the  color- 
blind. 


136  COLOR-BLINDNESS  : 

In  a  review  of  articles  on  color-blindness,  pub- 
lished in  the  "  Revue  des  Sciences  Medicales,"  Oc- 
tober, 1878,  Dr.  Javal  says  of  Delboeuf 's  method,  — 

"  I  obtained  sheets  of  gelatine  stained  with  fuchsine,  which 
produced  the  same  effect  as  Professor  Delboeuf's  solution, 
and  which  were  much  more  manageable.  But,  notwithstand- 
ing this  better  arrangement,  I  much  doubt  if  this  means  of 
correction  of  color-blindness  has  a  great  future;  for  the 
majority  of  those  affected  are  too  habituated  to  live  with 
their  infirmity  to  be  willing  to  suffer  the  slightest  incon- 
venience in  correcting  it.  This  correction  will  therefore  be 
only  applicable  to  those  persons,  relatively  few,  whose  occu- 
pation is  such  that  their  infirmity  is  a  positive  hinderance. 
And  from  these  should  be  excluded  railroad  employes, 
pilots,  &c.,  who  are  color-blind,  as  such  must  be  absolutely 
removed  from  j)osts  where  their  deficient  chromatic  sense 
may  cause  accidents." 

In  reference  to  Delboeuf  and  Spring's  state- 
ments as  to  chloride  of  nickel  in  solution,  —  one 
part  in  weight  to  twenty-five  of  water,  —  I  must 
say  I  have  carefully  followed  their  experiment,  as 
also  with  a  stronger  solution  arranged  as  they 
describe  ;  but  I  obtained  no  such  effect  as  they 
report,  —  of  thereby  rendering  the  normal  eye 
color-blind.  All  normal-eyed  with  whom  I  have 
tried  it  tell  me  the  same.  It  did  not  interfere  with 
my  sorting  the  worsteds  with  Holmgren's  test  per- 
fectly. Looking  through  such  a  solution  dulls  the 
red  a  little,  but  nothing  more  so  far  as  I  can  yet 
see ;  with  which,  as  I  said,  others  agree.  More- 
over, the  effect  of  the  fuchsine  solution  was  not 
negatived  by  it  to  the  color-blind.  I  confess  my- 
self at  a  loss  to  understand  Delboeuf's  statements. 


ITS   DANGERS   AND   ITS    DETECTION.  137 


CHAPTER  XIV. 

DANGERS   ARISING  EROM  COLOR-BLINDNESS. 

The  mortification,  inconvenience,  and  loss  of 
position  or  employment,  from  the  lack  of  power  to 
choose  proper  or  appropriate  colors  in  dress  and 
costume,  to  distinguish  and  match  colored  goods, 
to  mix  or  use  colored  pigments,  I  have  already 
sufficiently  described.  The  dangers  to  which  the 
community  are  subjected  from  color-blind  railroad 
employes  and  pilots  will  be  explained  in  this  chap- 
ter, and  how  and  wh}'-  these  should  be  avoided  by 
the  action  of  the  community  in  protecting  itself. 
For  instance,  an  engineer  has  run  on  one  road  for 
some  five  or  ten  years  without  accident  of  impor- 
tance. The  superintendent  requires  him  to  pass 
examination  by  an  expert,  who  finds  he  is  markedly 
red-blind,  and  shows  it  most  convincingly  to  the 
officials  of  the  road.  It  becomes  known ;  and  they 
then  do  not,  of  course,  dare  to  keep  him  in  his 
place.  He  is  dismissed,  to  protect  the  community 
from  danger. 

We  need  no  better  proof  of  the  recognition  of 
the  danger  than  the  measures  so  rapidly  taken 
for  the  last  two  years  on  so  many  of  the  Euro- 


138  COLOE-BLINDNESS  : 

pean  roads,  and  which  are  being  initiated  by  the 
others. 

Our  very  practical  American  people  have  recog- 
nized the  danger  from  numerous  colored  lights  or 
signal-flags  in  having  gradually  discarded  them. 
Many  roads  already  use  only  red  by  night  or  day. 
Green  and  red  are,  however,  most  generally  used 
to  signify  safety  and  danger.  From  experiment 
and  experience  I  agree  that  they  are  right.  We 
cannot  give  up  color  for  form  by  night.  It  is, 
however,  possible  by  day.  Is  the  danger  any  less 
great  here  in  the  United  States  ?  I  believe  the 
danger  from  ignorance  of  its  existence  is  not  small. 
The  chief  of  the  Brotherhood  of  Locomotive  En- 
gineers told  me  he  had  not  heard  of  color-blindness, 
although  he  had  run  an  engine  twenty  years ;  and 
asked  me,  with  some  feeling,  whether  I  "  thought  a 
man  was  fit  to  run  an  engine  who  could  not  tell 
green  from  red." 

The  Massachusetts  Board  of  Railroad  Commis- 
sioners reported  to  me  (Feb.  17,  1877),  that  "the 
subject  of  color-blindness  is  one  which  has  never 
come  to  the  attention  of  the  board ; "  and  they 
"  have  not  known  of  the  subject  being  investigated 
in  this  country." 

There  is  danger  from  color-blindness,  also,  from 
the  general  and  the  scientific  press  never  having 
taken  it  up  in  discussion  in  this  country.  I  am  at 
present  unacquainted  with  any  thing  on  this  special 
topic,  except  one  or  two  brief  articles  in  "The 
Chicago  Railway  Review,"  "  The  Scientific  Amer- 
ican," and  an  occasional  paragraph  in  some  medi- 
cal journal.  So  far  as  I  know,  the  whole  question 
of  color-blindness  and  its  natural  danger  was  first 


ITS   DANGERS    AND   ITS    DETECTION.  139 

publicly  discussed  by  myself  March  7,  1877,  be- 
fore the  Boston  Society  of  Natural  History,  and 
previously  at  a  scientific  club,  where  the  necessity 
of  a  color-test  examination  was  urged.  I  speak  of 
this  only  as  showing,  that,  notwithstanding  the 
number  of  very  competent  ophthalmic  surgeons  in 
the  larger  cities  of  the  Union,  the  subject  has 
failed  as  yet  to  arise  for  discussion  through  their 
efforts.  We  naturally  should  have  looked  to  them 
for  warning  from  the  danger,  especially  as  their 
daily  practice  renders  them  so  familiar  with  color- 
blindness from  injury  or  disease.  The  subject,  I 
confess,  forced  itself  on  my  attention. 

Thanks  to  the  efforts  of  such  men  as  Drs.  Wil- 
son, Favre,  Donders,  and  Holmgren,  railway  and 
marine  collisions  or  accidents  will  now  be  investi- 
gated in  relation  to  color-blindness ;  and  when  one 
is  proved  amongst  us,  as  they  have  been  elsewhere, 
to  have  occurred  on  this  account,  then  the  com- 
munity will  be  suddenly  awakened  to  a  realization 
of  the  danger  they  have  always  incurred,  and  cor- 
porations forced  to  make  some  effort  to  avoid  simi- 
lar accidents  in  future.  Then  will  be  brought  for- 
ward the  facts  presented  in  this  volume.  And  it 
will  be  shown,  that,  through  the  efforts  of  some 
railway  surgeons  and  scientific  men,  the  world  has 
been  taught  that  color-blindness  exists  to  a  greater 
or  less  degree  certainly  in  one  in  twenty-five  of  the 
whole  male  population ;  that  this  must  hold  good, 
therefore,  among  railroad  employes  and  mariners, 
where  it  is  a  source  of  very  great  danger.  Hence 
a  court  or  jury  will  not  be  slow  to  accept  and 
apply  the  verdict  of  the  general  community,  that 
Jhe  accident  was  preventable^  and  the  corporation 
liable. 


140  COLOR-BLINDNESS  : 

The  teacLiing  the  community  cannot  be  done  by 
the  single  or  united  efforts  of  scientific  men.  By 
examinations  in  the  schools,  a  knowledge  of  color- 
blindness and  its  dangers  can  be  disseminated,  as 
well  as  the  individual  warned  of  his  defect.  If  the 
medical,  popular,  and  daily  press  would  take  the 
subject  up,  as  they  did  in  Sweden,  the  railroads 
would  soon  feel  forced  to  act  immediately  in  the 
matter.  It  also  would  not  be  long  before  an  in- 
ternational commission  would  be  appointed,  and 
laws  for  the  control  of  color-blindness  in  the  ma- 
rine iMrsonnel  agreed  upon.  Professor  Wilson 
closes  his  book  with  the  following  :  — 

"  The  professions  for  which  color-blindness  most  seriously 
disqualifies  are  those  of  the  sailor  and  railway  servant,  who 
have  daily  to  peril  human  life  and  property  on  the  indica- 
tion which  a  colored  flag  or  lamp  seems  to  give.  Fortunate- 
ly a  ship  is  seldom  under  the  guidance  of  a  single  person; 
and  in  her  majesty's  vessels  the  color-signal  men  are  selected 
from  a  large  number,  and  are  ascertained  to  have  a  quick 
eye  for  color,  hi  merchant-ships  the  choice  must  necessarily 
be  made  from  a  much  smaller  number ;  and  the  appalling 
yearly  list  of  lost  vessels  which  appears  in  our  wreck  re- 
turns awakens  the  suspicion  that  more  than  one  of  these 
fatal  disasters  may  have  resulted  from  the  mistaken  color 
of  a  lighthouse,  beacon,  or  harbor-lamp,  which  on  a  strange 
coast,  and  with  x^erhaps  the  accompaniments  of  a  snow-storm 
or  a  thick  fog,  has  been  wrongly  decii^hered  by  a  color-blind 
pilot. 

"  On  railways  the  danger  attending  mistakes  of  signals  is 
much  greater  than  at  sea;  especially  in  this  country  (Eng- 
land), where  trains  travel  at  a  very  high  rate  of  speed,  and 
succeed  each  other  at  very  short  intervals.  ...  I  am  happy 
to  say  that  the  publication  of  my  papers  has  induced  the 
Great  Northern  Hallway  Company  to  require  that  in  future 
all  their  porters  shall  be  tested  as  to  their  freedom  from 
color-blindness  before  they  are  admitted." 


ITS   DANGERS   AND   ITS   DETECTION.  141 

The  attention  of  railroad  managers,  and  also 
that  of  the  community  at  large,  has  in  Europe 
been  repeatedly  called  to  the  great  danger  likely 
to  arise  from  color-blindness.  I  would,  for  in- 
stance, refer  to  Xoel,  in  the  "  Courier  des  Sci- 
ences ;  "  and  I  would  particularly  call  attention 
to  the  efforts  of  Dr.  A.  Favre  of  Lyons,  France. 
I  cannot  do  better  than  quote  from  the  resume  of 
his  memoirs.     He  says,  — 

"I  have  proved,  by  facts  personally  observed  from  1855, 
to  1873-77,  the  necessity  of  testing  for  color-blindness  all 
candidates  for  railroad  service,  and  the  exclusion  of  those 
who  are  red-Mind ;  also  the  necessity  of  specially  examining 
employes  who  have  been  injured  about  the  head,  those  re- 
covered from  severe  illness,  smokers,  and  drinkers.  I  call 
also  for  the  periodic  examination  of  all  in  active  railroad 
service.  The  majority  of  these  precautions,  adopted  on  the 
Lyons  road  since  1857,  have  been  gradually  enforced  on 
other  lines,  and  quite  recently,  also,  on  the  Belgian  roads. 
.  .  .  Feb.  8,  1875,  I  called  the  attention  of  the  '  Conseil  de 
Sante  des  Armees  '  to  the  use  of  the  colored  signals  em- 
ployed in  war,  and  the  necessity  of  testing  those  giving  or 
receiving  orders  by  colored  signals.  ...  In  February,  1875, 
I  called  the  attention  of  the  Medical  Society  of  Lyons  to 
color-blindness  caused  by  injuries.  .  .  .  On  Xov.  4,  1875,  I 
addressed  the  Medical  Society  of  Marseilles  in  reference  to 
color-blindness  in  navigation.  My  conclusions  were  adopted, 
and  communicated  to  the  marine  authorities  of  the  port  and 
the  minister  of  marine.  At  the  same  time  the  Academy 
of  Sciences  and  Letters  of  Lyons  voted  to  call  to  my  publi- 
cation the  attention  of  the  ministers  of  public  instruction, 
public  works,  war,  and  marine." 

Wilson  says,  — 

"  The  majority  of  even  color-blind  persons  are  able  to 
distinguish  bright  red  from  bright  green  when  they  are 
near  the  eye  and  well  illuminated  :  but  this  power  of  distin- 
guishing between  these  colors  diminishes  with  great  ra- 
pidity when  they  are  removed  to  a  distance  from  the  eye ; 


142  COLOE-BLINDNESS  : 

so  that  a  separation  of  a  few  feet  or  a  few  yards,  according 
to  the  severity  of  the  case,  abolishes  all  sense  of  distinction 
between  red  and  green.  As  the  colored  day-signals  on  rail- 
ways—  especially  the  flags,  which  alone  are  available  in 
some  of  the  most  pressing  emergencies — soon  tarnish  and 
darken,  the  effect  of  time  is  to  change  light  reds  and  greens 
into  mnch  darker  shades,  and  thereby  continually  to  diminish 
the  distance  (small  at  the  best)  at  which  the  two  danger- 
signals  can  be  distinguished  from  each  other  by  a  color-blind 
observer." 

The  danger,  therefore,  depends  on  the  number 
of  color-blind  emplo37ed  on  the  railroads.  They 
have  been  found  as  frequent  there  as  elsewhere. 

My  friend,  Dr.  Edmund  Hansen,  a  distinguished 
ophthalmic  surgeon  of  Copenhagen,  Denmark, 
writes  me,  June  24,  1877,  — 

"  The  railways  of  Denmark  are  in  the  possession  of  two 
parties  :  one  is  a  private  company,  which  owns  the  railways 
of  the  larger  island  called  Seeland,  and  of  the  adjacent 
smaller  islands,  Laaland  and  Falster ;  whereas  the  railways 
on  the  island  Funen  and  on  the  peninsula  Jutland  belong  to 
the  government.  The  investigation  for  color-blindness  has 
just  been  completed  by  the  private  companies :  on  the  govern- 
ment railways  it  will  be  done  in  the  course  of  the  summer. 
(I  will  give  you  the  results  of  the  private  company,  and 
shall  send  you  the  other  when  the  results  have  been  made 
known.)  The  examination  on  the  Seeland,  Laaland,  and 
Falster  roads  has  been  made  according  to  the  method  of  Pro- 
fessor Holmgren.  1,084  persons  were  examined,  of  whom 
50  were  women.  Of  this  number,  31  men  (or  2.87  per 
cent)  were  color-blind, — all  congenital  cases.  None  of  the 
women  were  color-blind.  Of  the  31, 10  were  perfectly  color- 
blind, 21  imperfectly.  Of  the  perfectly  color-blind,  6  had 
red-blindness,  4  green-blindness.  Their  occupations  were : 
2  station-masters  perfectly  green-blind ;  1  engineer  perfectly 
red-blind;  1  train-conductor,  1  fireman,  perfectly  green- 
blind  ;  4  jDorters,  3  blacksmiths,  7  railway  guards,  of  whom 
2  were  perfectly  red-blind  ;  2  assistants,  1  pupil,  perfectly 
red-blind ;  1  concierge,  2  foremen,  of  whom  1  was  perfectly 


ITS   DANGEES   AND  ITS   DETECTION.         143 

green-blind ;  4  workmen  on  station,  1  perfectly  red-blind  ;  2 
extra  conductors,  1  perfectly  red-blind." 

These  examinations,  I  understand,  were  made 
by  Dr.  Fontenay. 

Professor  A.  Quaglino,  of  Milan,  Italy,  writes  me, 
Aug.  11,  1877,  "I  do  not  know  whether  there 
are  any  statistics  of  color-blindness  published  in 
Italy,  though  I  am  sure  that  all  the  railroad  em- 
ployes are  subjected  to  a  rigorous  examination  in 
reference  to  their  color-perception." 

Dr.  J.  Stilling,  of  Cassel,  also  writes  me,  Dec.  6, 
1877,  "  I  have  but  once  had  opportunity  of  ex- 
amining railroad  employes,  about  four  hundred  in 
number.     Of  these,  six  per  cent  were  color-blind." 

Dr.  Magnus  reports  the  result  of  one  of  his  col- 
leagues on  a  Breslau  road  as  four  per  cent  of  color- 
blindness among  the  employes. 

Professor  F.  C.  Donders  of  Utrecht,  Holland, 
with  the  assistance  of  twelve  physicians  and 
ophthalmic  surgeons,  whom  he  had  specially  in- 
structed in  a  method  of  his  own,  examined  2,203 
employes  on  the  Holland  roads.  He  found  152  of 
these  more  or  less  color-blind.  These  he  subse- 
quently —  with  his  assistant.  Dr.  Bouvin  —  still 
more  carefully  tested,  thereby  confirming  his  pre- 
vious results. 

Dr.  A.  von  Reuss  writes  me  March,  1879,  having 
found  3.50  per  cent  color-blind  among  800  of  the 
employes  of  one  of  the  Vienna  roads. 

I  have  perhaps  quoted  enough  to  show  by  sta- 
tistics, and  by  the  precautions  railroad  corporations 
in  Europe  are  taking,  the  extent  to  which  color- 
blindness prevails  amongst  employes,  and  its  con- 
sequent danger.     But  I  should  quite  fail  in  giving 


144  COLOR-BLINDNESS  : 

the  subject  due  prominence  as  to  the  prevalence 
of  color-blindness,  the  value  of  scientific  investi- 
gation in  detecting  it,  its  danger  for  the  commu- 
nity, and  the  success  of  true  methods  of  testing 
in  convincing  railroad  people  of  all  this,  &c.,  were 
I  not  to  quote  from  Professor  Holmgren's  work. 
He  says,  — 


accident  at  Lageiiunda,  in  Ostrogothia,  Nov.  15,  1875,  and 
which  excited  great  public  attention,  there  was  evidence 
leading  me  to  suppose  that  color-blindness  was  one  of  the 
principal  causes  of  the  disaster.  This  led  me  to  think  that 
control  should  be  exercised  among  railroad  employes  as  to 
color-perception . 

"  In  June,  1876,  I  had  an  opportunity  for  testing  this  mat- 
ter. By  the  courtesy  of  Major-Gen.  von  Knorring  and 
Major  Rudbeck,  I  was  permitted  to  examine  2,200  men  of 
the  infantry  and  dragoons  of  the  guard  in  camp  in  Upland. 
From  this  examination  we  learned,  in  reference  to  the  ex- 
istence of  color-blindness  among  the  population  of  the 
province,  that,  out  of  the  2,200  men,  11  were  red-blind,  17 
could  not  perceive  green,  and  1  violet  (?)  ;  31  besides  were 
incompletely  color-blind  in  accordance  with  my  classification. 
There  were,  then,  60  defective,  or  2.7  per  cent.  The  cases 
of  '  feeble  sensation  of  colors  '  are  not  here  included. 

"July  14  of  the  same  year  I  had  opportunity,  at  the 
Scandinavian  Medical  Congress  assembled  at  Gothenburg, 
to  describe  my  method,  report  the  results  of  its  employment, 
and  also  to  express  my  views  as  to  the  necessity  of  taking 
measures  on  a  large  scale  in  reference  to  the  detection  of 
color-blindness,  especially  among  railroad  employes.  In 
consequence  the  congress  voted  unanimously  on  the  necessity 
of  instituting  examinations  to  detect  color-blindness,  first, 
among  railroad  employes ;  second,  among  pilots,  lighthouse- 
keepers,  and  sailors  in  general ;  and,  third,  in  the  schools. 
During  the  congress  I  had  time  to  show^  the  i^hysicians  the 
practical  application  of  the  method,  by  examining  in  their 
presence,  by  permission  of  Col.  Carlsohn,  100  men  of  the 
artillery  regiment  in  Gotha,  amongst  whom  we  found  4 


ITS   DANGERS    AND   ITS   DETECTION.  145 

color-defective,  —  1  for  red,  1  for  green,  and  2  incompletely- 
blind  to  color.  At  the  same  time  I  found  one  green-blind 
among  the  physicians,  members  of  the  congress,  and  one 
red-blind  among  the  assistants. 

"I  was  then  prepared  to  apply  directly  to  the  railroad 
administration.  Thanks  to  the  press,  which  followed  atten- 
tively the  discussions  in  the  congress  of  Gothenburg,  the 
question  came  to  the  knowledge  of  the  public.  It  naturally 
attracted  the  attention  of  the  railroad  officials,  who  for  the 
most  part  looked  upon  it  with  a  certain  distrust,  as  rather 
the  result  of  learned  imagination  or  over-solicitude  than  as 
a  practical  matter  for  the  railroad  service.  We  have  heard 
a  railroad  official  use  almost  literally  these  words :  '  If 
color-blindness  really  exists,  it  cannot  be  amongst  the  em- 
ployes, or  it  would  have  been  noticed.  This  must  at  least 
be  the  case  with  the  engineers  and  conductors,  all  of  whom 
obtain  their  places  after  passing  through  inferior  grades, 
and  consequently  after  having  sufficiently  proved  their  fac- 
ulty of  distinguishing  colors.'  It  was,  therefore,  very  impor- 
tant to  obtain  some  certain  data  on  this  point.  This  soon 
arose.  Mr.  Jacobsson,  chef  d^ exploitation  of  the  Upsala-Gefle 
line,  asked  me  to  accompany  him  on  a  tour  of  inspection, 
and  examine  all  the  employes  under  his  orders.  The  tour 
was  undertaken  in  tlie  fall.  We  left  Upsala  Sept.  7,  and,  to 
carry  out  our  examinations,  halted  at  all  the  stations,  at  all 
the  guard-houses,  and  at  every  gate ;  in  short,  we  stopped  at 
every  point  where  an  employe  was  to  be  found.  The  exami- 
nation was  finished  at  Gefle  Sept.  8.  All  the  force  —  266 
men  and  women  —  were  tested.  Amongst  them  we  found 
13  defective  ;  viz.,  4.8  per  cent.  Six  were  completely  green- 
blind,  and  7  incompletely  color-blind.  Their  positions  were, 
1  chief  of  station,  1  engineer,  2  conductors,  1  chief  of  equip- 
ments, 2  men  of  the  equipment  department  (one  a  supernu- 
merary), 2  overseers,  2  road-guards,  1  clerk,  and  1  stoker. 
Immediately  after  the  examination,  the  chef  d' exploitation 
dismissed  all  those  who  were  blind  for  green. 

"  This  first  expedition  was  interesting  in  many  respects. 
It  showed  that  the  method  of  examination  was  adapted  to, 
and  could  be  used  on,  the  railroads.  It  showed,  moreover, 
that  there  were  really  color-blind,  in  nearly  every  degree, 
employed  on  the  Swedish  roads,  of  which  no  one  had  had 
the  slightest  suspicion." 


146  COLOE-BLINDNESS  : 

Professor  Holmgren  reports  later  in  September, 
1878,  having  to  date  tested  7,953  railroad  employes, 
and  found  171  color-blind,  or  2.15  per  cent ;  viz., 
45  red-blind,  48  green-blind,  and  70  incompletely 
blind. 

"Ill  Finland  Dr.  L.  Krohn,  who  was  by  correspondence 
instructed  in  the  method  and  principles  applied  in  Sweden, 
has  ah'eady  examined  the  personnel  attached  to  the  rail- 
roads of  his  country.  A  locomotive  and  car  were  placed 
at  his  disposition  to  enable  him  to  test  the  employes  on  the 
whole  length  of  the  line.  It  was  completed  in  twelve  days. 
He  found,  among  1,200  persons  tested,  60  color-blind ;  namely, 
5  per  cent.  They  were  as  follows  :  4  red-blind,  25  green- 
blind,  and  31  incompletely  blind." 

Professor  Holmgren  brought  this  matter  before 
the  various  railroad  directions  in  Sweden.  More- 
over, experiments  vrere  made  in  the  Physiological 
Institute  at  Upsala;  so  that,  by  Nov.  9,  1876, 
throughout  Sweden,  it  was  ordered  that  all  the 
railroad  employes  should  be  tested  for  color-blind- 
ness by  the  methods  there  used.  What  Professor 
Holmgren  has  accomplished  leaves  no  excuse  for 
our  American  railroads  in  hesitating  or  refusing  to 
thoroughly  and  jDro^^erly  test  all  their  employes  for 
defects  of  color-perception,  and  dismissing  those 
who  are  color-blind,  and  providing  also  for  the 
future  by  testing  all  applicants  for  employment. 

If  long  before  this  my  readers  have  been  aston- 
ished at  the  facts  here  collected,  they,  no  doubt, 
have  also  been  equally  disposed  to  question  them, 
or  at  least  their  practical  bearing.  They  will  natu- 
rally say,  "  We  do  not  hear  of  railroad  accidents 
from  color-blindness,  and  rarely  of  marine  collis- 
ions attributable  to  this  cause."  Of  this  I  shall 
again  speak ;  but  I  must  first  here  explain  how  it  \^ 


ITS   DANGERS   AND  ITS   DETECTION.         147 

that  the  color-blind  employes  get  on  so  well,  con- 
ceal their  defect,  and  perhaps  avoid  accident.  I 
shall  confine  my  remarks  to  the  railroad  personnel 
and  mariners.  How  the  color-blind  escape  detec- 
tion in  every-day  life,  I  have  already  fully  de- 
scribed. Professor  Holmgren  explains  this  so  read- 
ily from  his  experience,  that  I  do  best  to  first  quote 
from  him.     He  says,  — 

"  We  should  imagine  a  color-blind  railroad  employe  would 
be  immediately  detected,  or  would  have  at  least  discovered 
his  own  defect.  This  very  natural  idea  has  greatly  tended 
to  retard  the  reform  we  have  called  for.  It  is,  however,  in- 
correct, and  does  not  stand  the  test.  On  the  contrary,  exami- 
nations showed  that  a  large  number  of  color-blind  were  em- 
ployed in  nearly  all  the  positions  on  a  railroad,  without  they 
or  others  being  aware  of  their  faulty  color-perception.  And 
further:  a  number  of  these,  far  from  being  convinced  of 
their  defect,  even  after  the  examination,  insisted  on  repeat- 
ing the  test  (even  six  or  seven  times),  giving  all  sorts  of 
excuses  in  explanation  of  their  constant  mistakes.  They 
all  agreed  in  saying  that  they  had  excellent  sight,  never  had 
experienced  the  slightest  difficulty  in  distinguishing  the  sig- 
nals, and  though  a  long  time  in  service,  and  in  most  impor- 
tant posts,  as  locomotive-engineers  for  instance,  never  had 
made  the  slightest  mistake. 

"  Certainly  we  may  well  be  astonished  at  this  condition 
of  things,  and  very  naturally  ask  how  it  is  possible  for  any 
one  to  perform  the  duty  of  engine-driver,  for  instance,  any 
length  of  time  without  exposing  a  deficiency  of  vision  so 
important  for  the  performance  of  this  duty.  There  are,  so 
far  as  we  know,  only  two  explanations :  one  is  in  the  pecu- 
liar visual  sense  of  the  color-blind,  and  the  exercise  of  this 
sense  in  distinguishing  the  signals  ;  while  the  other  depends 
on  the  conditions  under  which  an  engine-driver  ordinarily 
does  duty. 

"  As  to  the  first  explanation,  we  must  remember  that  every 
color  coming  from  an  illuminated  colored  surface  may  be 
more  or  less  bright  or  dark,  and  every  lantern-light,  even 
colored,  may  be  stronger  or  weaker.     Hence,  'in  a  colored 


148  COLOR-BLINDNESS  : 

object  or  colored  light,  the  eye  does  not  alone  take  note  of 
the  color  or  quality  of  the  light,  but  also  of  its  quantity  or 
intensiti/.  AVhen  two  objects  or  two  lights  appear  of  the 
same  color  to  the  eyes  of  a  color-blind  person,  they  may 
differ  as  respects  intensity.  This  being  the  sole  difference 
between  these  lights,  it  is  particularly  noted;  and  thus, 
often  as  a  result  of  special  exercise,  such  color-blind  person 
may  strengthen  his  perception  so  as  to  in  a  certain  degree 
make  up  for  his  color-deficiency.  He  resembles  somewhat 
the  persons  who,  deprived  of  one  sense,  replace  it  to  a  de- 
gree by  the  greater  exercise  of  one  or  more  of  their  other 
senses.  We  have  already  noticed  this  point,  so  very  impor- 
tant in  practice,  but  could  not  refrain  from  again  reverting 
to  it  here.  Any  one  who  has  experience  from  conversation 
with  intelligent  color-blind,  or  experimenting  with  Max- 
well's rotating  disk,  will  have  noticed  their  peculiar  sensi- 
tiveness to  varying  intensity  of  lir/Jit  whilst  comparing  two 
colors,  and  hence  can  have  no  doubt  as  to  how  a  color-blind 
person  can  so  often  distinguish  between  railroad-signals,  and 
give  the  colors  their  true  names. 

"  Did  we  not  know  this,  we  should  be  greatly  astonished 
to  find  with  what  facility  a  color-blind  railroad  employe  can 
distinguish  between  the  red  and  green  flag,  and  generally 
call  the  red,  green,  and  yellow  lanterns  by  their  right  color : 
but  it  is  the  intensity  of  the  light,  and  not  the  color,  which 
governs  his  decision  ;  and  tJiis  is  the  tvhole  secret.  The  flags 
and  lanterns  have,  in  fact,  usually  a  constant  difference  as 
to  intensity.  The  green  flag  is  to  the  color-blind,  as  also  to 
the  normal  eye,  undoubtedly  of  the  deepest  or  darkest  color, 
and  the  red  the  most  brilliant.  As  to  the  lanterns,  the  red- 
blind  always  recognize  the  red  light  by  its  being  darker  than 
the  green,  and  the  yellow  by  its  being  clearer  or  more  bril- 
liant than  the  other  two.  The  green-blind  finds  also,  in  his 
turn,  the  red  more  brilliant  than  the  green,  and  distin- 
guishes it  by  this. 

"The  other  explanation  lies  in  the  conditions  under  which 
an  engineer  has  to  observe  the  signals.  First  of  all,  we 
must  remember  the  great  regularity  with  which  all  the 
details  of  railroad  service  take  place.  An  engineer  starting 
from  a  station  at  one  end  of  the  line  knows  very  well  in 
advance  what  stations  to  stop  at,  and  which  to  pass.     Under 


ITS    DANGERS    AXD   ITS   DETECTI02>r.  149 

ordinary  circumstances  he  knows  which  light  ought  to  be 
exhibited  on  the  signal-posts  above  the  several  stations. 
The  hand-lanterns  are  not  as  important,  since  their  color  is 
not  so  essential,  being  supplemented  by  movements.  Hence 
it  is  only  under  exceptional  conditions  that  accidents  can 
happen  at  stations  from  mistakes  as  to  the  color  of  fixed 
lights.  There  may,  of  course,  be  a  number  of  other  cases 
exceptional  to  the  ordinary  regularity :  but  we  must  here 
notice  one  circumstance,  which  probably  has  been  and  still 
is  of  very  great  importance  ;  namely,  that  the  engineer  is 
not  the  only  one  who  has  to  watch  for  the  signals.  There 
is  always  with  him  the  stoker,  and  near  him  a  conductor,  an 
oiler,  &c.,  to  aid  him  at  critical  moments.  It  must  be  ex- 
tremely rare  that  all  the  personnel  of  a  train  are  affected 
with  color-blindness. 

"  Considering  only  practically  the  fact  mentioned,  and  the 
explanation  we  have  given,  one  might  perhaps  imagine  that 
color-blindness  had  some  scientific,  but  hardly  any  practical, 
interest,  and  hence  that  all  the  talk  that  has  been  made 
about  its  existence  among  railroad  employes  in  our  country- 
was  unnecessary ;  because,  as  may  be  said,  the  color-blind 
have  often  been  employed  a  long  time  in  railroad  service 
without  its  being  noticed,  and  without  accident  or  the  slight- 
est inconvenience  arising ;  and  finally,  that,  since  they  can 
really  distinguish  the  signals  (although  this  is  otherwise  than 
by  color),  their  kind  of  blindness  need  not  call  for  any  pre- 
ventive measures.  It  is  thus  that  a  great  many  persons  still 
reason. 

"  We  do  not  stop  here  to  give  the  testimony  of  experience 
on  this  point  in  our  country.  One  fact  is  certain  ;  namely, 
that  color-blindness  in  other  countries  has  caused  numerous 
and  very  fatal  accidents.  Even  if  this  had  not  been  defi- 
nitely proved,  it  is  none  the  less  evident  that  we  have  no 
right  to  await  another  such  experience  before  passing  to 
words  and  acts,  and  in  every  way  showing,  that,  notwith- 
standing the  numerous  circumstances  which  assist  th©  color- 
blind in  responding  to  the  signals,  danger  is  not  wholly 
avoided,  and  the  uncertainty  remains.  This  is  readily 
shown.  Xeither  the  fact  that  the  color-blind  have  been 
employed  many  years  on  the  railroads  without  causing  ac- 
cident, or  even  without  their  defect  being  discovered,  nor 


150  COLOE-BLINDNESS  : 

the  circumstances  we  have  cited  in  explanation  of  this  fact, 
furnishes  the  least  assurance  of  security. 

"  A  typical  color-blind  person  cannot  distinguish  between 
red  and  green.  This  is  an  incontestable  fact,  readily  ex- 
plained by  theory,  and  sufficiently  proved  by  experience. 
All  his  judgment  as  to  the  difference  of  colors  rests,  in  con- 
sequence, on  conjecture.  If,  perhaps,  exercise  enables  him, 
up  to  a  certain  point,  to  distinguish  between  the  red  and 
green  railroad  lights,  this  is  dependent  on  the  intensity  of 
the  light  telling  him  the  color.  But  there  is,  of  coarse, 
great  uncertainty  in  this  means  of  reading  the  signals  ;  and 
the  man  who  may  be  right  in  a  certain  number  of  special 
cases  will  surely  go  wrong  in  some  other.  It  is  a  principle 
not  dependent  on  theory,  but  confirmed  by  our  experience  in 
examining  more  than  two  hundred  color-blind ;  and  we  may 
extend  it  beyond  the  limits  we  have  here  kept,  —  in  other 
words,  to  the  majority  of  cases  also  of  incomplete  or  partial 
color-blindness. 

"  That  the  situation  of  the  color-blind  in  respect  to  sig- 
nals may  be  thoroughly  understood,  we  must  here  add  a  few 
important  words  on  the  point.  What  is  the  intensity  of 
light V  Strictly  speaking,  it  is  nothing  but  the  force  of  the 
impression  of  the  light  which  our  eye  receives.  This,  how- 
ever, is  dependent  on  two  factors,  —  one,  the  quantity  of  light 
radiating  from  the  object  observed  or  reflected  by  it ;  the 
other,  the  strength  or  amount  to  which  the  eye  re-acts  to 
this,  or,  in  other  words,  the  sensibility  of  the  subjected  vis- 
ual sense.  We  may  readily  understand  that  both  of  these 
factors  are  extremely  variable  under  the  circumstances  of 
the  engineer's  service.  The  amount  of  light  which  comes 
to  his  eye  depends  naturally  on  the  amount  reflected  from 
the  colored  object,  or  which,  for  example,  radiates  from  a 
railroad-lantern.  It  is  very  evident  that  this  quantity  may 
vary  from  many  causes,  such  as  the  nature  of  the  illuminat- 
ing material  and  the  wick,  the  coloring  matter  of  the  glass, 
its  thickness,  the  peculiar  property  of  the  glass,  &c.  If  a 
little  moisture  or  smoke,  vapor,  ice,  snow,  &c.,  adheres  to 
the  glass,  the  lantern  is  less  luminous.  A  lantern  illumi- 
nates differently  in  clear  from  what  it  does  in  foggy  weather. 
All  this  may  give  rise  to  mistakes.  But,  on  the  other  hand, 
the  sensibility  of  the  eye  differs  greatly  under  different  cir. 


ITS  DANGERS  AND   ITS  DETECTION.  151 

cumstances.  The  nervous  apparatus  of  the  eye  may,  like  all 
other  parts  of  the  system,  vary  in  its  sensitiveness.  The 
same  light  is  brighter  to  a  healthy  eye  in  repose  than  to  an 
eye  fatigued  and  weakened.  Every  modification  of  the  in- 
tensity of  the  light  is,  however,  for  the  color-blind  a  clionge 
in  color.  From  this  we  may  judge  how  little  dependence 
can  be  placed  upon  a  recognition  of  the  signals  which  the 
color-blind  gain  from  exercise. 

"  Hence,  if  we  admit  among  a  large  number  of  color-blind 
an  extraordinary  faculty  gained  by  the  exercise  of  the  eye 
with  different  degrees  of  intensity  of  light,  we  must  equally 
deny  that  this  is  sufficient  for  the  security  of  the  roads,  as 
we  cannot  be  assured  of  all  the  lantern-flames  being  of  the 
same  strength ;  all  the  glass  of  the  same  kind,  of  the  same 
thickness,  purity  of  color,  allowing  the  radiation  of  the  same 
quantity  of  light ;  and,  finally,  of  the  eyes  of  the  employes 
being  always  at  rest  to  the  same  degree,  this  being  practi- 
cally impossible.  '  No  person  in  his  senses  would  deliber- 
ately trust  his  life  in  the  hands  of  an  engineer  who  could 
only  distinguish  the  signals  by  the  difference  in  the  inten- 
sity of  the  light.  Ask  any  superior  official  of  a  road  if  he 
would  be  willing  to  take  charge  of  and  run  a  locomotive, 
assuming  the  responsibility,  when  uncolored  signals  alone 
were  permitted, and  a  feeble  light  meant  '■danger,''  a  medium 
one  '  attention  or  caution,''  and  a  strong  one  '  road  clear.'  If 
he  says-iiO,  tell  him  that  these  are  just  the  conditions  under 
whicbb  ev^ry  color-blind  engineer  has  performed  his  duties. 
The  absurdity  is  evident  at  once. 

"  The  aid  an  engineer  can  expect  from  those  within  his 
reach  is  as  little  to  be  depended  on  as  the  intensity  of  the 
light,  especially  as  he  himself  is  directed  to  observe  the 
signals,  and  is  responsible  for  what  happens.  Without  no- 
ticing all  the  possible  cases  when  he  may  at  the  moment  of 
danger  find  himself  without  help,  it  will  suffice  to  mention 
bnt  a  single  one ;  namely,  when  his  neighbors  are  also  color- 
blind like  himself. 

"  To  sum  up :  we  may  grant  that  a  number  of  circum- 
stances concur  in  rendering  railroad  accidents  from  color- 
blindness of  the  personnel  relatively  rare,  even  when  no  meas- 
ures have  been  taken  to  avoid  them,  and  experience  has 
fortunately  confirmed  this  opinion  ;  but,  on  the  other  hand, 


152  COLOE-BLINDXESS  : 

it  is  self-evident  that  such  accidents  may  happen  sometimes. 
Here  also  experience  testifies;  and  there  are  probably  many 
more  accidents  due  to  this  cause  than  those  proved  to  have 
so  occurred.  Under  these  circumstances  it  is  the  absolute 
duty  of  railroad  managements  and  maritime  authorities  to 
look  to  it  that  no  measure  which  can  aid  in  avoiding  the 
possibility  of  these  accidents  shall  be  neglected,  and  to  do 
all  in  their  power  to  guard  the  lines  of  communication  in 
the  land  and  on  the  sea  against  all  the  dangers  which 
menace  them." 

Direct  testimony  on  these  points  is  of  so  much 
value,  that  I  quote  from  Dr.  Magnus,  who  says,  — 

"  I  knew  an  engineer  who  was  red-blind.  Red  and  green 
were  absolutely  undistinguishable  to  him  ;  yet  he  could  tell 
the  red  from  the  green  signal,  from  having  cultivated  his 
perception  of  the  difference  in  the  intensity  of  the  light. 
However  valuable  this  capacity  may  be  for  the  individual 
color-blind,  there  is  danger  in  it.  It  may  happen  —  and,  no 
doubt,  often  does  —  that  the  color-blind,  by  the  cultivation 
of  their  power  of  appreciating  varying  intensities  of  light, 
conceal  their  defect,  and  induce  their  surroundings  to  sup- 
pose that  they  are  normal-eyed.  But  this  cultivated  power 
of  distinguishing  the  lights  by  difference  of  intensity  must 
always  be  a  very  unsafe  artifice,  which  succeeds  a  hundred 
times  to  fail  the  hundred  and  first.  It  is,  therefore,  a  very 
critical  thing  for  a  color-blind  railroad  employe  —  for  in- 
stance, an  engineer  —  to  be  able  to  conceal  his  defect  for  any 
length  of  time.  So  long  as  he  does,  so  long  are  the  trains 
in  danger  under  his  control ;  for  how  readily  may  his  artifice 
fail  him  by  which  alone  he  distinguishes  the  red  and  green 
signal-lanterns  from  each  other!  Only  the  most  careful  ex- 
amination of  all  railroad  employes  can  protect  the  public, 
which,  thanks  to  our  railroad  authorities,  is  now  conducted 
on  all  the  German  lines." 

Dr.  Minder,  in  Berne,  reports  among  his  cases 
that  of  "a- very  intelligent  young  man  who  was 
red-blind,  but  was  not  aware  of  it.  He  held  the 
position  first  of  fireman,  and  then  of  engineer, 
on  one  of  the  Swiss  roads.     He  was  hardly  at 


ITS   DANGERS   Ai^D   ITS   DETECTION.  153 

work  before  his  defect  troubled  him.  Thinking^  it 
was  due  to  the  spirit  he  drauk,  he  stopped  this  for 
a  while ;  but,  the  trouble  continuiDg,  he  became 
convinced  that  'something  was  wrong  with  him 
about  the  colors,'  and  left  the  distinguishing 
the  signals  to  his  normal-eyed  assistant.  When 
another  man  took  this  assistant's  place,  — who  also 
seems  to  have  been  color-blind,  —  the  work  began 
to  be  'uncomfortable.'  As  our  red-blind  engi- 
neer now  had  no  control  by  his  side,  and  very 
frequently  was  mistaken  in  his  decision,  there 
occurred  a  series  of  mistakes,  fortunately  only 
•whilst  manoeuvring  in  the  stations,  which  brought 
him  occasional  fines  and  other  disagreeable  con- 
sequences. 

"  The  red  signal-lantern  gave  him  the  most 
trouble,  because,  as  he  said,  he  could  only  distin- 
guish it  when  so  near  with  his  engine  as  not  to  be 
able  to  stop,  and  hence  run  by  it.  He  did  better 
with  the  green  signal ;  and,  when  asked  why,  re- 
plied, '  Because  it  was  brighter.'  To  the  question 
how,  then,  could  he  tell  the  green  signal  from 
white,  he,  in  a  roundabout  way,  compared  green 
to  weak  white ;  and  stated,  that,  with  a  lantern  of 
white  glass,  he  could,  by  screwing  up  and  down 
the  wick,  and  thereby  changing  the  amount  of 
the  light,  himself  imitate  the  usual  railroad-sig- 
nals. Very  bright  light  was  white;  very  weak 
light,  red;  medium  intensity,  green,  —  quite  cor- 
responding to  Holmgren's  statements  based  on 
theory.  The  seeming  impossibility  of  his  power 
of  distinguishing  being  dependent  on  the  amount 
or  intensity  of  the  light,  induced  me  to  search 
farther,  and  ascertain  what  a  complete  color-blind 


154  COLOR-BLINDNESS  : 

understood  by  pure  white.  I  found  for  this,  also, 
much  greater  color-sense  than  the  normal-eyed 
possess.  A  whole  series  of  color-blind  were  ex- 
pressly asked  to  select  only  the  purest  white. 
Of  worsteds  and  papers  they  picked  out,  besides 
the  white,  several  shades  of  bright  green,  gray, 
pure  gray  and  dirty  gray,  light  rose,  and  very  light 
violet. 

"  The  possibility  that  a  color-blind  may,  through 
his  life,  under  favorable  circumstances,  remain 
undiscovered,  and  as  engineer  or  switchman  per- 
form his  duty,  cannot  be  denied.  That  the  filling 
such  posts  by  the  color-blind,  however,  is  a  con- 
stant source  of  danger,  can  be  readily  under- 
stood. For  instance :  a  white  lantern  exposed  to 
the  weather  by  snow  or  rain,  by  the  absorption  of 
light  from  the  dimmed  glass,  may  appear  green 
to  a  color-blind  who  depends  upon  the  intensity 
of  the  light  alone.  So  also  a  green  light  may  give 
the  impression  of  a  red  one.  By  the  accidental 
use  of  thicker  or  darker  green  glass,  or  thinner 
and  brighter  red  glass,  the  difference  in  the  inten- 
sity of  the  light  may  also  be  destroyed;  and  hence 
arise  all  the  conditions  for  the  occurrence  of 
dangerous  mistakes." 

There  is  a  point  in  reference  to  steam  worth 
mentioning  here,  —  viz.,  its  varying  color;  and 
hence  its  possibility  of  causing  mistakes.  Pro- 
fessor Forbes,  in  1839,  noticed  the  sun,  through  a 
column  of  steam  from  the  safety-valve  of  an  engine 
on  the  GreenwicK  Railway,  of  a  deep  orange-red 
color.  This  he  again  noticed  on  the  Newcastle  and 
Carlisle  road,  and  it  induced  him  to  experiment 
with  white   lantern-light   seen   through   escaping 


ITS   DANGERS   AND   ITS   DETECTION.  155 

steam.  It  appeared  red  under  certain  pressure  of 
the  steam,  and  also  green  or  violet  under  other 
pressure.  Mr.  R.  Phillips,  in  1852,  followed  this 
up,  and  found  that  the  transmitted  light  was  red ; 
and  the  reflected,  blue.  As  to  this.  Professor 
Wilson  well  remarks,  "  Now  it  must  often  fall  to 
the  lot  of  engine-drivers  to  watch  lamps  through 
such  an  atmosphere,  which  will  convert  the  (white) 
safety-signal  into  a  danger-signal,  completely  alter 
the  color  of  the  (green)  caution-signal,  and  so 
darken  the  aspect  of  the  (red)  danger-signal  as  to 
render  it  invisible." 

To  the  even  very  slightly  color-blind  this  will 
be  intensified,  and  to  the  completely  color-blind 
his  only  means  of  distinguishing  the  signals  will 
be  gone ;  viz.,  the  difference  in  the  intensity  of 
the  light. 

One  of  the  dangers  from  color-blindness  on  our 
railroads  arises  from  the  supposed  cure  or  pallia- 
tion of  it  by  exercise  of  the  i:>cT%onnel  with  the 
colored  signals,  &c.  Upon  this  latter  point  I  dwelt 
when  discussing  the  incurability  of  congenital 
color-blindness.  It  becomes  therefore  necessary 
to  here  criticise  Dr.  Favre's  ideas  and  proposals  in 
reference  to  such  exercise.  The  whole  matter, 
however,  is  put  so  practically  by  Professor  Holm- 
gren, and  is  of  such  importance,  especially  in  this 
country,  that  I  shall  quote  from  him.  In  his  criti- 
cism of  Dr.  Favre's  ideas,  after  speaking  of  the 
various  ways  the  color-blind  supplement  their  de- 
fect, he  says,  — 

"  The  color-blind  railway  employe  has  always  a  certain 
assistance  at  his  disposal  in  distinguishing  the  flags  by  day: 
for  he  sees  not  only  the  flags,  but  also  the  person  who  holds 


156  COLOR-BLINDNESS  : 

them ;  a  green  grass-plot,  a  tree,  a  house,  —  in  short,  ob- 
jects whose  color-name  he  already  knows.  The  importance 
of  this  is  the  greater  from  what  we  know  of  the  value  of  com- 
parison in  the  use  of  our  other  senses,  and  hence,  also,  of  our 
color-perception. 

"  From  this  it  might  be  judged  that  it  was  a  matter  of 
indifference  whether  the  color-blind  could  be  cured  by  exer- 
cise with  colors  or  not,  so  long  as  they  can  by  other  means 
distinguish  the  signals.  We  admit  they  are  thus  by  day 
less  liable  to  mistake  them ;  but  we  cannot  grant  more.  The 
color-blind  can,  however,  never  be  aure,  since  they  can  never 
calculate  beforehand  all  the  circumstances  leading  to  mis- 
takes. Sunlight  on  a  green  flag,  with  the  surroundings  in 
the  shade,  makes  it  appear  red  to  them  ;  or,  what  is  worse, 
the  red  flag  on  a  bright  day,  when  in  the  shade  and  the  sur- 
roundings bright,  will  appear  green. 

"  The  condition  is  much  worse  with  night  service.  No 
comparison  is  then  possible.  Only  the  light  itself  is  now 
visible ;  and  what  adds  to  the  difficulty  of  distinguishing 
the  color  of  a  lantern  as  compared  with  distinguishing  a 
colored  surface,  is  our  accustomed  way  of  using  our  senses. 
In  fact,  we  do  not  take  cognizance  of  the  action  of  our  sense. 
We  do  not  ever  think  of  the  light  radiating  from  or  reflected 
by  the  object:  we  rather  refer  all  these  to  the  object  itself, 
and  regard  them  as  inseparable  attributes  of  it.  We  recog- 
nize the  light  of  the  lantern,  without  thinking  of  the 
material  on  which  it  depends.  We  do  not  see  the  lantern 
or  the  flame  burning  in  it,  but  only  the  light  which  has 
neither  the  form  of  the  lantern  or  the  flame,  but  is  isolated 
and  immaterial  in  the  air.  Now  the  color-blind  must  dis- 
tinguish whether  this  is  strong  (colorless),  medium  (green), 
or  weak  (red).  This  is  asking  more  of  the  human  eye 
than  it  can  do  with  certainty." 

"  The  color-blind  are  therefore  more  often  mistaken  in 
distinguishing  colored  lights  than  colored  surfaces.  If  we 
show  them  one  of  the  lanterns,  they  cannot  distinguish  it, 
unless  previously  i^ractised.  Showing  them  the  red  and 
green  together,  or  in  rapid  succession,  they  generally  distin- 
guish these  from  each  other;  and,  if  we  tell  them  the  names, 
they  remember  and  call  them  correctly.  The  red-blind  find 
that  the  red  of   the  signal-lantern,  such   as  used  on  the 


ITS  DANGERS   AND   ITS   DETECTION.  157 

Swedish  roads,  is  darker  (that  is,  weaker  in  light)  than  the 
green.  The  latter,  however,  seemed  to  them  darker  than 
the  common  yellow  light.  The  green-blind,  on  the  other 
hand,  find  that  the  green  light  is  weaker  (that  is,  darker) 
than  the  red.  With  the  next  opportunity  these  color-blind 
find  the  same.  Railroad  employes  are  therefore  rather 
more  sure ;  yet  much  is  dependent  on  the  special  lanterns 
used.  One  familiar  with  the  nature  of  color-blindness  will 
do  better  to  use  lanterns  with  different  glass  from  that  com- 
monly employed,  when  desirous  of  exhibiting  the  precise 
character  of  this  defect.  Let  him  take  one  with  a  thin 
pale-red  glass,  and  another  with  thick  dark-green  glass. 
The  color-blind  will  then  readily  take  the  green  light  for 
red,  and  red  for  green  or  colorless.  If  the  glass  of  the 
green  light  is  smoked,  he  will  take  it  for  red.  Cover  the 
colorless  light  with  steam  or  dew,  and  it  appears  to  him 
green.  Or  let  one  do  as  I,  —  namely,  have  lanterns,  the 
glasses  of  which  are  prepared  for  this  purpose,  and  differ 
from  each  other,  some  having  colorless  or  so-called  smoked 
glass  of  varying  absorptive  power,  —  and  they  will  quickly  be 
convinced  that  the  color-blind  is  guided  in  his  decision 
solely  hy  the  intensity  of  the  light. 

"  Another  circumstance  assists  the  color-blind  in  telling 
the  lantern's  light  at  a  distance,  which  is  also  dependent  on 
the  intensity  of  the  light,  though  this  connection  is  not  at 
once  seen.  It  is  the  varying  way  in  which  the  light  radi- 
ates outwards.  This  radiation  is  most  intense  with  the 
ordinary  lantern,  since  this  is  the  brightest  (strongest  in 
light) ;  whilst,  when  the  lantern-light  is  weak  (red  or 
green),  the  radiation  is  very  little  or  nothing.  A  color-blind 
railroad  employe  told  me  he  thus  distinguished  the  signals. 
It  need  be  hardly  said  how  unsafe  this  is." 

"  We  see,  therefore,  that  practice  is  of  no  avail  for  the 
vXDlor-blind.  Otherwise  an  employe,  who  has  had  daily  ex- 
ercise with  the  colored  lanterns  for  a  series  of  years,  would 
have  been  cured  of  his  defect.  A  pretty  wide  experience 
has,  however,  shown  us  that  not  one  of  the  many  color-blind 
we  have  examined  stood  the  test.  We  must  confess  that  a 
large  number,  from  constant  practice,  had  attained  extraor- 
dinary facility,  and  frequently  told  the  colors  correctly." 

"  As  a  proof  that  comparison  plays  such  a  strong  part,  it 


158  COLOE-BLINDNESS  : 

is  often  necessary  to  make  special  choice  of  the  particular 
lanterns  for  the  test.  If  we  use  the  ordinary  lanterns,  the 
color-blind  will  only  make  mistakes  at  the  commencement. 
If  they  see  all  the  three  lantern-lights  together,  they  are 
deceived  much  more  seldom.  A  colorless  glass,  with  mois- 
ture on  the  surface,  will  at  first  be  readily  taken  for  green ; 
a  smoked  green  glass,  for  red." 

There  is  another  peculiar  danger  on  railroads. 
A  mixture  of  the  two  complementary  colors,  red 
and  green,  necessarily  employed,  produce  white 
light.  This,  of  course,  does  not  affect  the  color- 
blind in  the  same  way  as  the  normal-eyed;  yet  it 
adds  to  their  confusion.  The  law  of  the  mixture 
was  naturally  well-known ;  but  Mr.  W.  H.  Tyndal, 
in  1853,  first,  I  think,  called  attention  to  its  Yevy 
practical  bearing.     He  says,  — 

"  Now,  we  have  this  curious  fact,  that  on  the  railways  the 
union  of  the  two  colors  —  the  primary  red  to  indicate  danger, 
and  the  secondary  gi^een  to  denote  caution  —  together  makes 
white,  the  signal  for  entire  safety.  This,  perhaps,  does  not 
practically  appear  in  experiment,  when  the  mind  is  on  the 
alert  to  distinguish  between  the  two  colors.  If  the  rays 
from  a  green  lamp,  such  as  are  used  on  railways,  are  thrown 
upon  a  white  board,  and  those  from  a  red  lamp  are  directed 
to  the  same  spot,  —  the  distance  of  the  two  lamps  from  the 
board  being  equal,  —  the  red  rays,  though  rendered  paler, 
predominate.  There  is,  in  fact,  too  much  red.  But  the 
red  lamp  may  be  removed  so  much  farther  from  the  board 
than  the  green  one  as  to  allow  the  green  rays  to  predominate; 
and  there  must  be  a  point  of  distance  where  neither  color 
would  predominate,  and  at  which  the  mixture  of  the  rays 
on  the  board  would  be  white.-  I  recently  made  an  experi- 
ment on  one  of  the  metropolitan  railways  with  a  green  and 
a  red  signal-lamp.  A  man  was  stationed  at  the  end  of  a 
tunnel,  about  four  hundred  yards  long,  and  directed  to  wave 
the  two  lights  together.  The  pointsman  at  the  other  end,  not 
knowing  any  thing  of  the  nature  of  the  experiment,  was 
asked  what  light  was  waved.  He  was  satisfied  it  was  white, 
and  could  not  be  persuaded  that  two  lights  —  a  red  and  a 


ITS  DANGERS   AND  ITS   DETECTION.  159 

green  —  were  really  used,  although  the  matter  was  afterwards 
explained  to  him.  Now,  it  may  sometimes  happen  that,  in 
rapid  travelling,  the  rays  from  a  red  lamp  and  a  green  one 
shall  flash  together  across  the  sight  of  an  engine-driver ;  or 
the  unsteady  motion  of  an  engine  may  render  the  driver  un- 
able 'to  see  distinctly  and  separately  two  signals  of  different 
colors,  the  rays  from  which  may  fall  upon  his  eye  in  parallel 
lines.  In  either  case  it  is  not  improbable  that  the  light 
might  be  regarded  by  him  as  white.  A  light  may  be  dis- 
cerned without  the  color  of  it  being  distinctly  seen.  In 
such  case  it  would  most  likely  be  regarded  as  white,  —  that 
being  the  most  common.  It  is  not  imi:)robable  that  some  of 
the  accidents  which  have  occurred  in  railway  travelling  have 
arisen  from  the  colors  of  the  lights  shown  being  indistinctly 
seen ;  perhaps  from  a  confusion  of  rays  from  two  or  more 
lamps.  In  some  cases  most  contradictory  evidence  has  been 
given  as  to  the  color  of  the  signal  shown.  The  subject  is 
perhaps  worthy  of  the  attention  of  railway  engineers." 

The  following  is  an  interesting  proof  of  liow  a 
shrewd  observer  may,  from  lack  of  knowledge  of 
the  peculiar  condition  above  explained  of  the 
color-blind's  perception,  fail  to  explain  cases  pre- 
sented to  him ;  — 

Mr.  Thomas  Nelson,  an  optician  in  Chicago,  111., 
in  an  article  in  "  The  Chicago  Railway  Review  "  of 
March  30,  1878,  says,  — 

"I  have  kept  records  of  various  accidents  that  have  oc- 
curred, both  upon  land  and  water  during  the  past  few  years ; 
and  I  have  gathered  such  information  about  some  of  them  as 
I  could  get  outside  of  official  sources.  Often  I  was  unable  to 
get  any  of  any  value ;  but  I  am  convinced  beyond  a  doubt 
that  a  large  proportion  of  them  could  have  been  traced  to 
color-blindness  for  a  correct  solution  as  to  the  primary  causes 
of  the  accident.  The  query  has  been  made,  that  if  these 
defects  in  their  various  forms  are  as  ni:merous  and  of  such 
a  dangerous  character  as  has  been  shown,  how  can  we  ac- 
count for  such  a  comparatively  small  number  of  accidents 
occurring  which  might  be  charged  to  them  ?  I  have  attrib- 
uted it  to  the  high  average  intelligence  and  acquired  cau- 


160  COLOR-BLINDNESS  : 

tiousness  of  engineers  and  ]pilots  as  a  class.  They  have  be- 
come so  accustomed  to  be  on  the  lookout  for  danger,  that 
their  suspicions  are  easily  aroused,  which  creates  a  sort  of 
instinct  that  governs  their  actions,  and  they  do  not  recognize 
but  that  their  perceptions  are  correct.  My  convictions  in 
this  respect  have  been  greatly  strengthened  within  the  past 
few  months,  there  having  been  related  to  me  some  experi- 
ence with  an  engineer,  who  was  continually  making  narrow 
escapes ;  and,  after  watching  his  actions  under  different  cir- 
cumstances for  a  time,  color-blindness  was  suspected,  proved, 
and  afterward  acknowledged  by  him.  The  correctness  with 
which  he  formed  conclusions  under  the  existing  circum- 
stances would  indicate  that  he  had  some  means  by  which  he 
was,  enabled  to  form  a  plan  of  action ;  but  he  declared  that 
he  had  nothing  upon  which  to  base  his  actions  but  the  cau- 
tiousness acquired  in  that  branch  of  service." 

The  means  he  had  to  assist  him  were  of  course 
the  to  him  varying  intensity  of  the  light,  when  red, 
green,  or  white.  This  is  an  interesting  proof  of 
how  totally  unaware  a  color-blind  may  be  of  the 
way  he  supplements  his  chromatic  defect,  as  also 
how  he  may  escape  detection. 


ITS   DANGERS   AND    ITS   DETECTION.  IGl 


CHAPTER   XV. 

DANGERS  FROM  COLOR-BLINDNESS  ON  THE  OCEAN. 

If  we  turn  now  from  the  land  to  the  sea,  we 
shall  find  the  dangers  from  color-blindness  as 
great,  or  even  greater.  The  largest  majority  of 
those  color-blind  are  so  for  red  and  green.  These, 
however,  are  the  colors  necessarily  chosen  by  all 
nations  to  be  by  law  carried  on  the  two  sides  of 
all  vessels  from  sunset  to  sunrise,  —  the  green 
light  on  the  starboard  side,  and  the  red  light  on 
the  port  side.  These  are  so  arranged  that  they 
can  only  both  be  seen  when  the  vessel  is  directly 
ahead,  and  far  enough  off  to  allow  us  to  see  both 
sides.  These  lights  show  us,  therefore,  the  position 
and  the  direction  of  motion  of  a  vessel.  Mistaking 
their  color  will  of  course  be  most  disastrous. 

Dr.  Romberg  has  classified  the  reports  of  some 
maritime  accidents  from  1859  to  1866.  They 
number  2,408. 

Want  of  skin,  or  carelessness,  of  the  ship  personnel, 
or  the  accidents  which  it  was  impossible  to  prevent 
or  avoid 1,562 

Error  of  the  pilot  or  captain      .....        215 

Want  of  observation  or  proper  interpretation  of  the 

rules  of  the  way   .......        537 

Undetermined  causes 94 


162  COLOE-BLINDNESS  : 

Under  the  last  tlu?ee  heads,  in  the  large  number 
of  846,  there  are  probably  some  attributable  to 
color-blindness.  They  all  are  not  accidents  from 
carelessness  or  want  of  skill;  for  those  are  in- 
cluded in  another  series. 

M.  Leonce  Raynaud  and  M.  Degram  have  dem- 
onstrated the  effect  of  fog  on  the  color  of  lights. 
Fog  or  mist  makes  white  lights  reddish.  In  thick 
weather  green  lights  appear  white.  A  sailing- 
master  meets  a  green  light  rendered  pale  by  a 
thick  night :  in  whatever  amount  he  is  color-blind, 
in  that  degree  will  the  light  appear  white  to  him, 
causing  most  dangerous  hesitation;  or,  even  if 
convinced  he  has  not  a  green  light  ahead  of  him, 
he  manoeuvres  as  if  it  were  a  red  one.  Color- 
blindness may  therefore  well  be  considered  as  one 
of  the  causes  of  collision  at  sea.  This  imperfec- 
tion may,  however,  occasion  the  loss  of  a  vessel  in 
another  way :  I  mean  in  the  recognition  of  lights 
on  the  coast,  &c.  Dr.  Feris  reports  three  cases  of 
such  mistake  from  the  *'  Annales  du  Sauvetage 
Maritime,"  vol.  iii.,  1873.     He  says, — 

"If  color-blindness  is  considered  a  grave  danger  on  rail- 
roads, how  much  more  on  the  »ea !  Colors  are  very  impor- 
tant to  the  mariner:  the  flags,  the  side-lights,  and  even  the 
lighthouses  and  buoys  and  beacons,  present  various  colors. 
It  is  impossible  for  a  helmsman  or  a  signalman  to  interpret 
or  transmit  signals  if  they  have  no  appreciation  of  color. 
Errors  with  flag-signals  are  not  so  likely  on  board  of  vessels, 
as  they  are  employed  in  daylight,  and  more  often  controlled 
by  officers  in  charge.  But  the  men  at  telegraph-stations  are 
often  alone,  not  under  observation,  and  hence  more  likely  to 
make  mistakes.  National  flags  may  be  mistaken,  but  more 
especially  the  white,  red,  and  green  Bengal  lights  used  as 
night-signals.  ...  If  good  color-perception  is  necessary  for 
a  helmsman,  how  much  more  for  the  commander  of  a  vessel  1 


ITS   DANGERS    AND   ITS   DETECTION.  163 

The  increase  of  collisions  at  sea  is  an  indisputable  fact. 
How  many  remain  unexplained,  or  referred  to  another 
cause,  which  are  no  doubt  due  to  the  color-blindness  of  a 
single  man !  " 

The  testing  for  color-blindness  Las  already  com- 
menced in  the  navies  of  Prussia,  Russia,  Norway, 
Sweden,  Denmark,  and  Austria.  My  friend.  Dr. 
Ed.  Hansen  of  Copenhagen,  writes  me,  June, 
1877,  — 

"  I  have  had  the  opportunity  of  examining  a  large  num- 
ber of  the  individuals  who  enter  the  royal  navy :  I  hope 
some  day  to  be  able  to  give  you  some  statistical  information 
on  this  point,  if  you  still  take  an  interest  in  it." 

Professor  Holmgren  reports  as  to  the  examina- 
tion of  4,225  Swedish  sailors,  finding  94  (or  2.22 
per  cent)  color-blind. 

Dr.  Lederer  was  appointed  by  the  medical  de- 
partment of  the  Austrian  navy  to  test  sailors  at 
the  naval  station  at  Pola.  He  examined  of  the 
sailors  at  the  station  and  on  the  artillery  school- 
ship  "  Adria  "  1,312,  finding  63  (or  4.8  per  cent) 
color-blind.  There  has  been  some  misunderstand- 
ing as  to  his  report  due  to  his  employment  of  Stil- 
ling's  cards  and  pieces  of  colored  glass  and  paper, 
instead  of  Holmgren's  infinitely  more  sure  and 
ready  method  with  the  worsteds. 

Dr.  Feris  of  the  French  navy  found,  among  501 
of&cers  and  men,  47  "  who  presented  in  varying 
degrees  an  alteration  of  the  chromatic  sense." 
Their  ages  were  betw^een  seventeen  and  fifty  years. 

Dr.  Favre,  in  France,  records  the  examination 
of  1,050  men  for  the  navy  or  lighthouse  depart- 
ment, and  finding  61  (or  5.8  per  cent)  more  or  less 
color-blind.     In  discussing  the  question,  he  also 


164  COLOR-BLINDNESS  : 

makes  some  remarks  in  reference  to  the  loss  of  the 
French  steamer  "  Ville  du  Havre  "  by  collision 
with  an  English  sailing-vessel.  This  fearful  acci- 
dent most  painfully  interested  us  Bostonians,  since 
so  many  were  lost  from  our  midst  in  that  ill-fated 
vessel.  I  have  frequently  expressed  in  private 
my  own  suspicions  that  the  accident  may  have 
been  caused  by  color-blindness;  but  I  will  here 
simply  quote  Dr.  Favre  :  — 

"  After  the  loss  of  the  '  Ville  du  Havre/  the  newspapers 
which  described  the  collision  stated  most  positively  that  the 
green  light  was  not  recognized  in  time.  If  the  steamer's 
officers  and  crew,  who  should  have  seen  the  signal-light, 
were  never  tested  for  color-blindness,  there  is  one  chance  in 
twenty  that  the  officer  or  sailor  whose  duty  it  was  could 
not  distinguish  green,  and  one  in  seventy-five  that  he  would 
confound  this  color  with  red.  We  know  how  the  matter 
ended.  The  English  admiralty  decided  that  the  English 
vessel  was  free  from  all  blame,  and  the  French  admiralty 
declared  that  the  French  vessel  could  not  be  in  any  way 
criminated.  No  one  thought  of  attributing  the  mistake  to 
the  very  probable  one  of  color-blindness." 

I  lately  had  curious  proof  of  the  color-blindness 
of  a  sea-captain,  who,  I  understand,  has  now  retired 
from  active  service.  He  was  in  the  habit  of  work- 
ing worsteds  to  while  away  the  monotony  of  a  sea- 
voyage.  These  worsteds,  however,  always  had  to 
be  picked  out  for  him,  and  the  colors  marked,  to 
avoid  his  making  mistakes. 

Dr.  Daae  of  Kragero,  Norway,  in  a  lecture  on 
color-blindness,  given  April  10,  1878,  before  the 
Medical  Society  of  Christiana,  says,  — 

"  We  must  admit  that  the  possibility  of  confounding  the 
signal-lanterns  in  general  is  not  so  great  on  the  railroads  as 
on  the  sea.  On  the  roads  the  glass  of  the  lanterns,  at  least 
within  the  limits  of  each  countrv,  has  a  somewhat  definite 


ITS   DANGEES   AXD   ITS   DETECTION.  165 

red  or  green  color,  which  even  those  quite  color-blind  learn 
to  distinguish  by  the  difference  in  the  intensity  of  the  light. 
The  signals,  moreover,  come  at  stated  times  and  places, 
so  that  it  is  known  where  they  are  to  be  expected  ;  and  thus 
they  can  be  seen  and  distinguished  at  leisure,  as  it  were. 
Not  so  on  the  ocean.  In  the  lanterns  of  the  various  vessels 
the  color  of  the  green  or  red  glass  varies  considerably.  The 
green  glass  varies  also  more  in  intensity  than  tone,  Xow 
let  us  suppose  no  signal-light  has  been  seen  for  some  little 
time,  when  suddenly  a  red  or  green  one  appears,  and  but 
one.  The  question  is  then.  Is  this  a  red  or  green  light? 
The  vessels  are  close,  and  instant  decision  is  necessary.  Or 
several  lights  are  seen,  and  the  ship  we  are  in  is  sailing  be- 
fore the  wind,  and  hence  bound  to  keep  out  of  the  way. 
Most  old  sailors  can  remember  cases  where  those  on  board 
were  not  agreed  as  to  the  color  of  a  lantern. 

"  But  how  can  having  rules  for  the  marine  of  one  country 
only  be  of  avail?  On  the  ocean  vessels  from  all  parts  of 
the  world  pass  each  other.  When  two  vessels  meet,  it  will 
help  but  little  if  the  officers  and  crew  of  but  one  vessel  have 
normal  color-perception.  If  there  are  color-blind  on  the 
other  vessel,  collision  may  occur. 

''  As  to  the  railroads,  it  is  not  of  such  importance  that 
the  requirements  as  to  color-blindness  should  be  the  same  in 
all  countries.  If  one  country  has  one  set  of  regulations,  and 
another  a  different  one,  whilst  the  third  requires  no  exami- 
nation, it  concerns  only  the  individual  country  itself.  But,  as 
to  the  marine,  it  is  necessary  to  have  an  international  law." 

The  test  for  color-blindness  now  being  so  simple 
as  to  be  reaclilj  carried  out  by  the  surgeons  at- 
tached to  vessels,  especially  naval  medical  officers, 
there  can  be  no  great  difficulty  in  having  an  in- 
ternational commission  meet,  and  frame  the  laws 
which  shall  govern  all  the  navies  and  merchant- 
marine  of  the  great  maritime  nations  at  least.  It 
would  then  be  as  readily  recognized  that  every 
officer  and  man  must  be  as  able  to  perfectly  distin- 
guish the  red  and  green  lights  as  to  know  where 
they  belong,  and  what  they  mean. 


166  COLOR-BLINDNESS 


CHAPTER   XVI. 

CAN  THE   RAILROAD    AND    MARINE    SIGNALS     BE 
CHANGED  ? 

I  HAVE  given  the  statistics  of  the  frequency  of 
color-blindness  in  Europe  from  many  observers, 
and  in  this  country  from  my  own  tests.  Its  fre- 
quency, also,  among  railroad  employes  and  sailors 
has  been  proved  by  Euro]3ean  research ;  unfortu- 
nately not  yet  in  the  United  States.  I  do  not 
think  any  one  will  now  doubt  that  from  two  to  five 
per  cent  of  the  men  absolutely  daily  employed  on 
the  railroads  in  this  country  are  probably  color- 
blind. This  granted,  we  are  at  once  asked.  Why 
not,  then,  use  some  other  colors  besides  red  and 
green?  and,  when  this  is  answered,  why  not  use 
form  instead  of  color,  or  the  grouping  of  several 
white  lights,  &;c.  ? 

I  was  long  ago  convinced  theoretically  of  the 
possibility  of  substituting  form  for  color  by  day  on 
the  switches,  and  equally  of  the  imjjossibiliti/  of 
substituting  any  other  colors  for  red  and  green  as 
night-signals.  Experiment  and  observation  have 
now  convinced  me  practically  that  the  railroads 
can  use  form  instead  of  color  by  day,  and  can  not 


ITS   DANGERS   AND  ITS   DETECTION.  167 

substitute  form  for  color  by  night.  Reel  and  green 
are  the  colors  which  we  must  select  as  being  most 
in  contrast,  and  also  for  many  practical  reasons 
in  reference  to  the  glass,  &c.  This  I  have  repeat- 
edly shown  at  scientific  societies.  Experiment 
also  has  proved  to  me  that  red  and  green  must  be 
used  as  night-signals  on  the  sides  of  vessels.  This 
matter  is,  however,  too  important  for  me  to  simply 
give  my  own  unsupported  opinion.  A  color-blind 
has  gravely  discussed  with  me  the  necessity  of 
changing  the  signals  to  meet  his  difficulty,  saying, 
"  It  was  not  right  to  throw  a  man  out  of  his  em- 
ployment for  a  congenital  defect,  incurable."  We 
have  no  better  authority  than  Professor  Holmgren, 
who  explains  and  discusses  this  question  of  other 
colors  or  form,  &c.,  so  thoroughly  and  so  practi- 
cally, that  I  must  quote  his  remarks  verbatim.  As 
to  the  modification  of  the  signal  system,  he  says,  — 

"  If  congenital  color-blindness  is  incurable,  —  or  at  least  if 
we  know  no  actual  remedy  for  it,  —  it  is  necessary  to  devise 
some  other  method  (while  retaining  the  color-blind  in  the 
employment  of  railways)  of  guaranteeing  the  communica- 
tions against  any  mistakes  they  might  commit  with  regard 
to  signals.  It  is  seen  by  what  precedes  that  these  errors  can 
and  must  occur  in  the  use  of  the  signal-colors  generally 
adopted,  —  red,  green  (and  yelloiv).  The  color-blind  has  only 
two  primitive  colors  ;  whilst  the  normal-eyed,  according  to 
the  Young-Helmholtz  theory,  has  three.  But  the  usual  rail- 
road signal-colors  are  just  those  primitive  ones  which  neither 
the  red  nor  the  green  blind  can  perceive.  This  choice  seems 
therefore  unfortunate.  Wilson  is  of  the  same  opinion.  If 
red  and  green  color-blindness  are  the  kinds  of  complete  or 
partial  blindness  which  are  most  generally  seen,  it  would 
seem  that  the  difficulty  might  be  considerably  diminished, 
if,  in  place  of  using  the  actual  colors,  those  should  be  se- 
lected best  suited  to  these  kinds  of  color-blindness,  although 
they  might  not  suit  the  third  kind  of  partial  color-blindness, 


168  COLOR-BLINDNESS  : 

or  violet-blindness,  which,  according  to  the  experience  ac- 
quired up  to  the  present  time,  relatively  very  seldom  occurs. 

"  Undoubtedly  the  principle  we  have  endeavored  to  es- 
tablish would  not  be  radically  enforced ;  but  the  practical 
result  at  least  would  be  comparatively  nearly  accomplished. 
As  the  color-blind  has  but  two  principal  colors,  or  two  classes 
to  which  he  can  refer  all  the  colors,  it  is  evident,  that,  to 
select  two  colors  that  he  can  recognize  and  distinguish  with- 
out the  least  hesitation,  it  would  be  necessary  to  select  one 
from  each  class.  In  this  way  it  is  always  possible  to  bear 
in  mind  that  each  kind  of  color-blindness  wdll  always  be 
able  to  find  two  colors  distinctly  defined,  but  not  more  than 
two.  It  is  therefore  necessary,  first,  to  ask  how  far  two  colors 
for  signals  could  satisfy  the  demands  of  railways  and  the 
navy.  As  regards  railways,  it  is  claimed,  and  it  may  be 
conceded,  that  in  case  of  necessity,  and  perhaps  without  too 
great  inconvenience,  two  colors  might  be  made  to  answer. 
It  is  certain  that  three  colors  are  a  great  improvement  upon 
two. 

"  It  is  scarcely  necessary  to  discuss  this  point,  since  it  is 
only  with  railroad-signals  as  wdth  all  other  signs  of  commu- 
nication,—  the  more  numerous  they  are,  the  more  serviceable 
are  they,  and  the  more  complete  can  be  the  communications 
they  give.  The  color-sense  is  the  best  proof  of  this ;  for 
certainly  the  normal-eyed,  with  three  principal  colors,  has  a 
more  complete  and  acute  impression  from  the  manifold 
colors  of  the  external  w^orld  than  the  color-blind  who  has 
but  two  fundamental  colors. 

"  Let  us  admit,  however,  that  tw^o  colors  would  answer, 
and  that  it  w^ere  desired  to  sacrifice  the  advantage  of  three 
colors  for  another  advantage,  —  namely,  that  of  retaining  in 
the  service  of  railways  the  color-blind :  there  will  still  re- 
main the  necessity  of  making  a  good  selection  of  these  two 
colors.  This  is  more  easily  said  than  done.  The  choice 
must  be  so  made  that  one  color  may  be  selected  from  each 
of  the  two  groups  in  which  all  the  colors  are  classed  ac- 
cording to  the  system  for  the  color-blind.  Now,  it  is  found, 
as  we  have  already  seen  in  the  instances  of  the  princij^al 
colors  of  the  red  and  green  blind,  that,  amongst  the  seven 
colors  of  the  rainbow  perceptible  to  the  normal  observer,  four 
—  namely,  red,  orange,  yellow,  and  green  —  belong  to  one 


ITS   DANGERS  AXD  ITS   DETECTION.  169 

class,  and  three  —  especially  blue,  indigo,  and  violet  —  to  the 
second.  Consequently,  one  of  the  colors  must  be  red,  orange, 
yellow,  or  green ;  and  the  other,  blue,  indigo,  or  violet.  It 
should  very  naturally  be  our  object  to  give  the  preference  in 
the  selection  to  the  colors  which  most  strongly  affect  the  eye 
at  the  time  of  the  comparison.  Xow,  the  most  intense 
colors  of  the  spectrum  —  that  is  to  say,  the  most  vivid  colors 
which  enter  into  the  white  light  of  the  sun  —  are  yellow  and 
blue,  one  of  each  of  the  two  groups.  We  then  select  them, 
the  more  willingly  that  the  light  of  the  lantern  is,  without 
any  preparation  and  to  a  very  high  degree,  yellow,  though 
it  is  not  homogeneous.  But  we  are  far  from  being  so  fortu- 
nate with  regard  to  blue.  We  here  encounter  a  difficultj^ 
on  the  contrary,  which  induces  us  to  doubt  whether  a  change 
of  colors  will  accomplish  the  desired  end. 

"  On  all  colored  surfaces  —  flags,  paintings,  semaphores, 
&c. — employed  by  railways  to  reflect  during  the  day  the 
sunlight  or  daylight,  the  proposed  colors  answer  perfectly 
without  any  doubt,  and,  in  all  probability,  no  color-blind 
individual  of  the  kinds  specified  would  nominally  make  mis- 
takes of  judgment.  But  the  night-signals  are  quite  another 
matter,  and  are  by  far  more  important  for  many  reasons. 
This  is,  therefore,  why  we  prefer  to  attach  here  so  much  im- 
portance to  them,  as  during  the  day  a  multitude  of  different 
circumstances  might  give  warning  of  danger,  while  during 
the  night  the  colored  light  is  the  only  signal  which  indi- 
cates it. 

"  The  colored  lights  used  for  night-signals  are  made,  as 
all  know,  by  placing  colored  glass  before  the  flame  of  a  lan- 
tern. The  use  of  Bengal  lights  as  regular  signals  could 
scarcely  be  introduced  into  practice.  Now,  a  colored  glass 
produces  a  colored  light,  because,  of  all  the  kinds  of  light 
radiated  from  the  flame,  but  one  kind  (or  at  least  mainly 
one  kind)  is  allowed  to  escape,  while  all  the  others,  or  a 
greater  part  of  the  others,  are  absorbed  by  the  glass.  Thus 
blue  glass,  according  to  its  thickness  or  degree  of  coloring, 
absorbs  all  the  other  kinds  of  light  emitted  by  the  flame  of 
the  lantern,  allowing  only  the  blue  rays  to  escape.  But, 
unfortunately,  as  is  well  known  by  direct  experience,  the 
flame  of  the  lantern  emits  comparatively  but  a  small  amount 
of  blue  light  when  rape-seed  oil  and  photogene,  or  generally 


170  COLOE-BLINDNESS : 

any  of  our  ordinary  sources  of  artificial  light,  are  employed ; 
and  this  is  vfhy  all  appear  yellow  or  red  when  compared  with 
the  light  of  day.  Under  such  circumstances  blue  glass  can 
naturally  transmit  only  a  small  amount  of  blue  light ;  and 
the  light  of  a  blue  lantern  must,  consequently,  always  be 
very  feebly  luminous. 

"  Of  course  the  intensity  of  the  light  will  greatly  depend 
on  the  thickness  of  the  glass.  But  what  is  gained  in  inten- 
sity by  a  thin  glass  is  lost  in  color ;  for,  whilst  thin  glass  in- 
creases the  intensity,  through  it  will  j)ass,  besides  the  fewer 
blue  rays,  also  the  red  and  green.  Hence  the  blue  rays  be- 
come, in  an  inverse  ratio  to  the  thickness  of  the  glass,  more 
like  those  from  an  ordinary  lantern,  and  therefore,  to  a  cer- 
tain degree,  white  light.  The  light  is  in  consequence  very 
weak,  since  only  enough  red  and  green  light  passes  through 
the  glass  to  balance  the  blue  rays. 

"What  we  have  just  said  of  blue  applies  equally  to  indigo 
and  violet.  The  proposed  changes  of  the  colors  of  signals 
furnishes,  therefore,  but  two  colors  in  place  of  three  ;  and 
then  one  is  a  very  feeble  light,  so  that  it  is  difficult  to  see 
it  far  off  when  sufficiently  colored.  This  state  of  things 
scarcely  holds  out  much  inducement  to  introduce  a  re- 
form of  this  nature.  And  it  seems  the  more  dangerous 
that  this  change  of  colors  in  the  signals  would  cause  those 
with  normal  sight  amongst  the  person?iel  to  run  the  same 
risk  that  the  really  color-blind  do  :  I  mean  that  they  would 
be  forced  to  distinguish  and  judge  the  night-signals  alone 
by  the  intensity  of  the  light.  The  safety  of  the  service,  as 
we  have  shown,  would  gain  nothing,  and  it  would  be  diffi- 
cult to  find  a  conscientious  man  desirous  of  continuing  his 
work  under  these  circumstances.  Such  a  reform  in  behalf 
of  the  color-blind  would,  de  facto,  shut  out  a  much  larger 
number  of  normal-eyed. 

"  We  have  heard  that  blue  lights  are  used  on  the  Ameri- 
can roads.  This  we  are  not  able  to  deny,  but  must  first  be 
assured  that  all  the  American  employes  can  distinguish  the 
signals  there  used,  and  then  learn  all  the  details  of  the  rail- 
road accidents  which  have  happened  in  that  country. 

"■  The  result  of  all  that  we  have  just  said  is,  it  seems  to  us, 
that  the  proposed  change  of  the  signal  colors  is  not  very 
practical,  ana  such  would  be  the  case  with  any  other  choice 


ITS   DANGERS  AND  ITS   DETECTION.  17l 

of  two  colors.  It  must  at  least  be  conceded  that  the  new 
signal-colors  would  be  to  every  normal  observer  worse  than 
those  now  in  use  with  us,  as  with  nearly  all  nations :  in 
brief,  if  they  were  adopted,  it  would  diminish  the  public 
safety.  We  must  add,  that,  by  adopting  them,  the  principle 
we  have  explained  is  not  taken  into  consideration,  according 
to  which  it  is  necessary  to  use  a  system  of  signals  adapted 
to  all  kinds  of  color-blindness,  since  the  violet-blind  are  not 
able  to  distinguish  between  yellow  and  blue.  The  proposed 
change  should  therefore  be  rejected,  it  seems  to  us,  on  every 
practical  consideration. 

"  (2d)  Colorless  Light  and  Darkness,  Black  and  White.  — It 
has  been  seen  that  it  is  impossible  to  hope  for  colored  signals 
suiting  every  one,  color-blind  or  not.  It  becomes  necessary, 
therefore,  to  try  to  devise  a  plan  for  establishing  a  system 
of  signals  independent  of  colors,  and  based  upon  the  intro- 
duction of  a  colorless  light  of  different  degrees  of  intensity. 
We  have  already  discussed  the  most  important  of  the  points 
in  reference  to  the  intensity  of  light.  While  there  is  noth- 
ing more  sensible  to  our  sight  than  the  relative  intensity  of 
two  lights  placed  side  by  side  (when  the  absolute  intensity 
does  not  exceed  certain  limits),  in  the  present  case  the  only 
comparison  involved  is  made  from  memory,  so  to  speak, 
which  is  equivalent  almost  to  an  appreciation  of  the  abso- 
lute intensity  of  light.  We  are  so  far  from  being  able  to 
judge  of  this,  that,  in  spite  of  a  deeply  felt  need  and  con- 
stant efforts,  science  even  has  not  succeeded  in  discovering 
suitable  measures  to  apply  to  it. 

'•  It  is,  however,  necessary  to  acknowledge  here  that  a  sys- 
tem of  signals  based  only  on  two  extremes  of  intensity  of 
light  —  namely,  on  light  and  darkness,  white  and  black — • 
ought  to  suit  the  normal  observer  as  well  as  the  color-blind. 
Moreover,  such  a  system  ought  to  satisfy  all  exigencies,  pro- 
vided it  is  practically  applied,  and  that  two  signals  only  are 
sufficient.  A  white  and  black  flag,  &c.,  would  fully  suffice 
during  the  day  :  but  such  would  unfortunately  not  be  the 
case  at  night;  for  a  black  light  is  a  contradiction  of  terms, 
and  it  would  be  necessary,  consequently,  according  to  this 
system,  for  the  night,  when  signals  are  of  the  greatest  impor- 
tance, to  be  limited  not  to  three,  but  to  one  signal  only,  unless 
the  absence  of  all  signals  could  be  considered  as  one.     Here 


172  COLOR-BLINDNESS  : 

it  might  be  well  asked,  whether  the  better  system  is  not  that 
which  is  based  on  the  alternations  of  darkness  and  light; 
that  is,  movable  signals- or  eclipsed  signal-lights.  But  we 
will  not  enter  a  field  unfamiliar  to  us.  We  cannot,  however, 
but  have  a  sensation  of  dread  at  recalling  the  various  arti- 
ficial means  railroad  management  would  have  to  depend 
upon  for  the  purpose  of  retaining  or  accepting  the  color- 
blind in  service.  As  far  as  we  know,  no  system  has  yet 
been  discovered,  based  upon  the  x^rinciples  alluded  to  above, 
which  could  advantageously  take  the  place  of  the  one  actu- 
ally in  use. 

"  (3d)  Form,  Movement,  Number.  — If  we  do  not  succeed  in 
finding  a  suitable  system  of  signals,  based  on  the  differences 
of  the  quality  and  quantity  of  light,  there  remains  but  to 
appeal  to  some  arrangement  in  space,  if  absolutely  limited 
to  the  visual  sense. 

"  Of  our  other  senses  in  reference  to  recognizing  signals,  we 
might,  besides  the  eye,  appeal  to  the  ear.  Both  can  receive 
impressions  from  a  great  distance.  But  for  our  purpose  the 
ear  is  still  less  adapted  than  the  eye ;  and  the  former  can 
only  be  regarded  as  secondary  for  certain  definite  purposes, 
or  at  short  distances.  For  example  :  in  foggy  weather  the 
whistle  and  bell  are  used,  &c.  Many  different  ways  suggest 
themselves  of  varying  the  signals  by  form  and  arrangement 
in  space  :  large  brilliant  surf  aces*  arranged  in  different  forms ; 
several  small  lights  grouped  in  different  positions  with  refer- 
ence to  each  other;  lights  simply  disposed,  but  differing  in 
value  as  signals  according  to  their  number,  or  else  illumi- 
nated figures  of  simple  colors,  and  produced  by  different 
movements,  and  so  on.  A  practical  difficulty  seems  to  be 
connected  with  such  a  system  :  the  signals  require  the  illu- 
minated surfaces  to  be  large  enough,  or  placed  at  distances 
considerable  enough  between  the  luminous  points,  to  appear 
distinctly  afar  off.  Now,  the  larger  such  a  figure,  having  the 
outlines  marked  with  luminous  points,  the  greater  the  risk 
that  a  portion  of  it  be  hidden  by  other  objects  intervening 
between  it  and  the  eye.  These  two  inconveniences  must  be 
apparent,  particularly  if  these  surfaces  and  illuminated  fig- 
ures have  to  be  placed  at  every  point  where  colored  lanterns 
are  found ;  as,  for  example,  on  locomotives  and  cars.  More- 
over, it  will  be  very  difficult  to  place  these  signals  at  all 


ITS   DAXGEES   AND   ITS   DETECTION.  173 

points  of  the  road  where  accidents  may  happen.  These 
doubts  are  perhaps  groundless,  and  possibly  better  not  ex- 
pressed, as  being  out  of  our  range. 

"  It  is  rather  our  purpose  to  discuss  this  point  generally, 
and  examine  it  scientifically.  We  would  say,  therefore,  that 
our  eye  can  more  readily  detect  difference  in  color  than 
difference  in  form.  The  reason  of  this  is  veiy  plain.  The 
retina  alone,  of  all  the  several  parts  of  the  eye,  must  be 
reached  by  the.  light,  to  give  us  a  definite  form  or  definite 
light.  For  the  light  to  reach  the  retina,  all  parts  of  the 
eye  in  front  of  it  must  be  transparent.  When  this  alone  is 
the  case  we  can  perceive  the  color  of  an  object  or  a  light; 
but  if  its  form  is  to  be  appreciated,  not  only  must  the  light 
reach  the  retina,  but  it  must  affect  it  strongly  and  definitely 
to  give  us  a  clear  picture  of  the  object.  The  difference,  as 
we  see,  is  great.  The  whole  dioptric  apparatus  of  the  eye  is 
necessary  for  the  form  of  an  object  to  be  perceived,  whilst 
such  apparatus  is  superfluous  for  simply  color-perception. 
The  greater  the  number  of  the  active  agencies  necessary  to 
accomplish  a  certain  M'ork,  the  greater  the  sources  of  error 
in  the  accomplishment  of  such  work.  All  organic  diseases 
of  the  cornea,  the  crystalline  lens,  or  the  vitreous  humor, 
hinder  the  perception  of  the  form  of  an  object,  but  not  of 
its  color.  The  advantage  as  respects  color-perception  from 
this  is  all  the  more  when  we  remember  that  the  most  fin- 
ished dioptric  apparatus  of  the  eye  is  relatively  imperfect ; 
and  this  imperfection  is  still  further  increased  by  many 
anomalies.  What  would  a  sailor  do  who  had  to  determine 
the  form  of  an  illuminated  object  by  the  help  of  a  poor  spy- 
glass, the  glasses  of  which  were  dirty,  broken,  or  badly 
ground  ?  Probably  he  could  not  do  it ;  whereas  he  could 
decide  the  color  of  the  light  in  spite  of  his  poor  instru- 
ment, which  would  simply  reduce  the  brightness. 

"  If  the  system  of  signals  were  based  upon  form,  and  all 
persons  discharged  from  the  service  of  railways,  who,  in  con- 
sequence of  an  imperfection  of  vision,  could  not  clearly  and 
decidedly  distinguish  these  signals  at  a  distance,  the  propor- 
tion of  such  would  be  larger  than  that  of  the  color-blind. 
To  form  an  idea  of  the  different  capacities  of  the  normal  eye 
in  the  various  senses  just  mentioned,  we  will  recommend  a 
very  simple  experiment.     Take  something,  —  colored  paper. 


174  COLOR-BLINDNESS  : 

for  example ;  make  some  plain  figures,  such  as  letters,  one 
of  which  must  be  attached  vertically  to  a  large  black  or 
•white  surface.  To  prevent  any  distraction  from  subjective 
influences,  let  some  one  else  select  and  attach  this  letter, 
while  the  observer  stands  at  such  a  distance,  that,  even  with 
the  eye  directed  toward  it,  but  a  single  object  can  be  seen. 
If  the  letters  are  small,  it  is  not  necessary  that  the  distance 
should  be  very  great.  Then,  if  the  symbol  be  slowly  ap- 
proached, v/ith  the  eye  fixed  on  the  colored  surface,  the 
following  observations  in  the  order  in  which  the  different  im- 
pressions succeed  each  other  v/ill  be  made :  When  the  letter 
is  first  perceived,  neither  form  nor  color  can  be  distinguished. 
Nothing  is  seen  but  a  point  or  patch  darker  than  the  back- 
ground, if  that  be  white;  or  lighter,  if  it  be  black.  The  first 
attribute  remarked,  as  the  distance  diminishes,  is  its  color. 
When  the  color  is  very  distinct,  it  is  necessary  to  approach 
considerably  nearer  before  the  form  is  perceptible ;  that  is 
to  say,  before  this  letter  can  be  read,  and  its  name  given. 
This  simple  experiment  clearly  shows  that  the  eye,  as  far  as 
it  is  possible  to  compare  its  capacities  in  different  directions, 
is  first  sensible  to  the  relative  intensity  of  light,  then  to 
color,  and  finally  to  form.  It  would  be  necessary,  of  course, 
to  consider  various  circumstances  relative  to  the  choice  of 
color,  form,  &c.,  if  the  experiment  should  be  made  with  ex- 
actness to  serve  as  a  basis  for  a  scientific  demonstration. 
What  we  have  said  suffices,  however,  to  point  out  what  di- 
rection a  reform  in  the  signals  should  take,  granting  that 
any  such  change  is  desirable.  If  a  signal  system  could  be 
found  and  practically  introduced  which  depended  on  light 
And  dark,  then  it  would  be  preferable  to  the  present  in  use. 
If  such  fails,  then  we  must  consider  the  present  as  the  most 
practical,  because  based  not  only  on  the  principle  of  the 
difference  in  the  quality  of  light, — that  is  to  say,  on  color, 
—  but  also  because  just  those  colors  have  been  chosen  Vvdiich 
practice  has  proved  to  be  best  suited  for  the  purpose.  Ex- 
perience also  seems  to  have  decided  in  favor  of  this  system; 
since,  in  spite  of  the  substitutes  proposed  with  a  view  to  re- 
tain the  color-blind,  it  has  up  to  the  present  time  maintained 
its  ascendency,  so  to  speak,  throughout  the  entire  world." 

As  I  have  already  said,  our  very  practical  Ameri- 


ITS   DANGERS   AXD   ITS   DETECTION.  175 

can  people  have  gradually  discarded  the  use  of  all 
but  red  and  green  lights  on  the  railroads,  with  but 
few  exceptions.  On  the  sea,  of  course,  the  use  of 
other  than  red  and  green  signals  is  impossible. 


176  COLOR-BLINDNESS 


CHAPTER  XVII. 

NECESSITY  AND   DIFFICULTY   OF   CONTEOL. 

Are  there  no  measures  now  taken  in  the  United 
States  to  avoid  danger  from  color-blindness  ?  will 
here  at  once  be  asked  of  me.  I  would  much  like 
to  have  been  able  to  report  on  the  some  two  hun- 
dred railroads  of  the  United  States  in  respect  to 
any  examination  of  their  employes  as  to  color- 
blindness. It  is,  however,  a  delicate  question. 
From  what  I  have  learned,  I  conclude  that  here 
and  there  railroad  superintendents  keep  it  in  mind ; 
and  when,  from  accident  or  otherwise,  suspicion  is 
aroused  in  reference  to  an  employe,  the  latter  is 
tested  by  the  superintendent  with  the  flags  or  lan- 
terns used  on  the  road.  This  suffices.  No  medical 
man  —  and  much  less  an  expert  —  is  called  upon 
to  decide.  If,  anywhere  in  this  country,  there  is 
at  this  time  any  thing  like  a  systematic  test  for 
color-blindness  of  the  j^ersonnel  of  the  road,  I  shall 
be  agreeably  surprised  to  learn  it.  There  may  be 
—  but  I  do  not  know  of  any  —  salaried  railroad 
surgeons  in  the  United  States,  whose  duty  is  wholly 
with  the  road,  and  who  could  learn  to  test  for 
color-blindness.     Even  when  a  test  of  an  employ^ 


ITS   DANGERS   AND    ITS   DETECTION.  177 

has  been  reported  to  me  as  made,  I  have  had  no 
proof  that  it  was  not  simply  lack  of  good  eyesight, 
and  not  lack  of  color-perception.  I  shall  be  only 
too  happy  to  be  corrected  by  the  management  if  I 
am  wrong  in  stating  that  the  railroads  of  this 
country  are  not  more  protected  from  the  danger 
of  color-blindness  than  were  the  roads  of  Europe 
before  the  very  recent  successful  systematic  efforts 
on  the  part  of  those  from  whom  I  have  quoted  in 
this  volume.  I  believe  practically  nothing  is  at 
present  sure  to  protect  the  community  in  this 
respect. 

In  the  merchant-marine  service  I  very  much 
doubt  if  it .  is  any  better.  I  have  been  told  by 
naval  officers  that  care  is  taken  in  this  respect  so 
far  as  to  look  out  that  the  men  make  no  mistakes 
as  to  the  port  and  starboard  lights ;  but  I  have  not 
learned  that  any  systematic  scientific  examination 
of  the  naval  2?erso7inel  is  carried  out  by  the  sur- 
geons of  the  navy.  I  believe  I  am  right  in  saying 
this  also  of  the  army.  But  both  army  and  navy 
surgeons  are  eminently  qualified  to  learn  and  use 
the  present  methods  of  testing  for  color-blindness, 
the  danger  from  which  they  can  equally  appreciate. 

The  government  cau,  and  no  doubt  soon  will, 
carry  out  proper  examinations  for  color-blindness 
in  the  army  and  navy.  General  national  laws  can 
also  be  enacted  as  to  the  merchant-marine ;  inter- 
national will  come  in  time  as  a  matter  of  necessity. 
The  difficulties  with  the  railroads  are,  however, 
very  great.  Here  the  interests  and  safety  of 
the  community  have  to  contend  with  ignorance, 
prejudice,  pecuniary  considerations,  and  incredulity 
born  of  supposed  immunity  from  danger.     These 


178  COLOR-BLINDNESS  : 

corporations  have  no  surgeons  attached  to  their 
roads,  who,  in  their  interests,  could  carry  out  proper 
examinations  to  both  protect  themselves  and  the 
community.  Even  when  interest  is  awakened 
from  acknowledged  danger  justly  feared,  railroad 
managers  are  very  likely  to  turn  to  any  one  calling 
himself  a  medical  man,  and  rely  on  his  statement 
as  to  his  ability  to  examine  and  pass  judgment  on 
their  employes.  Then,  when  they  are  satisfied 
from  his  reports  that  they  are  safe,  and  accident 
happens,  color-blindness  is  proved  in  the  employe 
before  the  court  and  jury,  and  at  once  undeserved 
miscredit  is  thrown  upon  the  surety  and  useful- 
ness of  such  examinations.  It  is  therefore  with- 
out hesitation  that  I  would  caution  as  to  the  choice 
of  those  to  be  engaged  in  testing  railroad  employes 
for  color-blindness.  The  life-insurance  companies 
of  the  country  recognize  this  most  thoroughly,  — 
so  much  so,  that  examination  for  life-insurance  is 
almost  a  specialty. 

We  can  scarcely  hope  for  such  practical  good 
results  as  were  shown  in  Sweden,  where,  by  the 
simple  efforts  of  one  scientific  man,  all  the  railroad 
employes  of  the  country  were  in  a  few  months 
tested,  and  laws  to  govern  the  future  made  and 
enforced ;  yet  exactly  the  same  is  possible  in  this 
country  as  there.  Either  the  state  governments 
or  the  state  railroad  commissioners  can  require 
thorough  examination  of  all  employes  for  color- 
blindness, or  the  railroad  managers  can  do  it  them- 
selves. It  is  with  some  natural  curiosity  that  the 
solution  of  the  problem  will  be  watched.  In  one 
of  these  ways  this  safeguard  to  travellers  must 
come,  since  they  will  learn  the  danger  they  incur 


ITS   DAXGEES   AND   ITS   DETECTION.  179 

as  quickly  as  the  railroad  corporations  the  danger 
they  subject  them  to,  not  to  speak  of  possible 
damages  recoverable  after  an  accident  due  to  color- 
blindness. Not  only  must  railroad  emploj-es  and 
mariners  have  good  eyesight,  but  they  must  be 
j)roved  to  have  normal  color-perception. 

Professor  Holmgren  is  at  the  head  of  the  control 
in  Sweden ;  and  his  practical  knowledge  and  ex- 
perience render,  of  course,  all  he  says  of  great 
value  to  us  about  to  commence  this  work  here  in 
the  United  States.     He  states  as  follows  :  — 

"Xo  half-way  measures  are  allowable.  All  employes 
with  defective  chromatic  vision  must  be  removed  from  posts 
of  danger.  They  should  be  required  to  distinguish  the  sig- 
nals by  their  color  as  the  normal-eyed  can.  The  violet-blind 
may  be  allowed  on  the  road.  This  defect  is  so  rare  as  to  be 
scarcely  ever  met  with.  There  are,  of  course,  positions  on 
the  road  not  requiring  the  reading  the  signals ;  but  it  is  a 
bad  plan  not  to  be  able  to  call  on  any  employe  in  an  emer- 
gency. Any  method  of  testing  for  the  elimination  of  the 
color-blind  will  be  in  place  which  is  tuto  cito  et  Jucunde, 
the  carrying  out  of  which  gives  the  best  results  in  the  quick- 
est time,  and  is  open  to  the  smallest  amount  of  difficulties 
and  misunderstandings.  It  must  not  fail  to  detect  a  color- 
blind, or  prove  that  an  employe  is  normal-eyed.  Whilst 
there  must  be  no  question  of  thoroughness,  it  is  to  be  re- 
membered there  are  hundreds  to  be  examined,  and  but  little 
time  can  be  given  to  each  individual.  We  cannot  have 
heavy  or  costly  apparatus  to  be  transported.  These  points 
are  to  be  considered  in  reference  to  any  method." 

"  Testing  should  be  only  in  the  hands  of  those  who  under- 
stand it.  On  the  roads  and  in  the  marine  the  surgeons  have 
the  scientific  knowledge  necessary  to  carry  out  examinations. 
On  board  ship  the  sailors  could  be  at  least  roughly  tested  by 
the  captain.  There  are  cases  where  a  specialist  would  need 
to  be  employed  to  decide  whether  color-blindness  existed  or 
not,  as  an  ordinary  surgeon  would  shrink  from  answering 
because  not  in  position  so  to  do.  So,  also,  a  specialist  would 
be  called  upon  to  decide  whether  the  defect  was  simulated." 


180  COLOE-BLINDNESS  : 

"  There  is  a  difference  to  be  made  between  those  in,  and 
those  seeking,  service.  The  latter  we  can  have  time  for  in- 
dividually. The  former,  when  a  general  examination  is 
undertaken,  requires  from  the  numbers  great  care  and  decis- 
ion. A  thorough  examination  w^ould  seem  to  insure  safety; 
but  acquired  color-blindness  must  be  remembered.  And  if, 
as  is  claimed,  color-blindness  may  grow  better,  it  also  may 
grow  worse  :  hence  the  necessity  of  continued  vigilance,  and 
watching  for  cases  from  disease  or  injury,  in  addition  to  the 
thorough  examination  for  all  congenital  cases.  The  possi- 
bility of  an  employe  claiming  to  have  been  made  color-blind 
by  accident,  after  having  been  received  into  service  and 
passed  his  color-test,  is  a  matter  also  to  be  thought  of. 
Color-blindness  from  railroad  injury  has  been  found  by  Dr. 
Favre  for  instance.  The  rights  and  claims  of  the  road,  or 
rather  the  public  and  the  individual,  are  often  nicely  bal- 
anced, and  great  circumspection  is  necessary.  Severe  dis- 
eases like  typhus,  as  well  as  injuries,  and  also  the  abuse  of 
spirit  and  tobacco,  cause  color-blindness.  Hence,  after  ac- 
cidents, the  personnel  interested  should  be  again  tested,  and 
always  any  drinking  men  or  heavy  smokers  quite  often 
looked  after." 

"  After  every  railroad  accident  or  collision  at  sea,  depend- 
ent in  whole  or  part  on  misunderstanding  colored  signals, 
not  only  must  the  men  directly  at  fault  be  tested,  but  also 
all  those  used  as  witnesses.  The  necessity  of  this  is  self- 
evident.  It  would  be  absurd  to  punish  any  one  because  a 
blind  man  says  he  saw  him  break  a  rule,  or  let  a  man  go 
free  because  a  blind  man  says  he  saw  him  obey  the  rule. 
The  same  as  to  color-signals :  no  witness  should  be  admitted 
who  is  not  proved  to  be  free  from  color-blindness.  This  is 
so  plain  that  discussion  of  it  seems  useless;  but  it  is  not 
recognized  by  the  guardians  of  the  law.  The  whole  ques- 
tion of  color-blindness  or  not,  when  claimed  or  denied,  must 
fall  within  the  province  and  decision  of  the  specialist 
alone." 

"  Granted  now  that  tests  are  introduced,  and  thorough 
examinations  carried  out  on  our  roads,  what  is  to  become  of 
the  color-blind?  The  defect,  we  know,  exists  in  all  degrees 
of  severity.  Whilst  there  will  be  no  doubt  of  the  necessity 
of   dismissing   the   large   majority,  the  decision  as  to  the 


ITS   DAKGERS   AND   ITS   DETECTION.  181 

others  can  be  determined  by  the  examiner  consulting  with 
the  management,  and  explaining  the  character  and  degree 
of  the  trouble.  The  possible  danger  of  the  incompletely 
color-blind  being  called  upon  to  decide  colors  quickly,  must 
never  he  put  out  of  sight,  and  this  may  occur  ichatever  his  position 
on  the  road." 

"We  would  again  repeat  that  it  is  the  interest  of  the  man- 
agement, as  well  as  of  the  public,  to  remove  absolutely  all 
difficulties  and  dangers  arising  from  color-blindness.  This 
end  cannot  be  considered  as  attained  so  long  as  a  single 
color-blind  employe  remains  in  service.  AVhen  all  color- 
blind are  eliminated  is  the  reform  first  commenced.  It  is 
no  less  necessary  to  carefully  test  periodically  those  with 
doubtful  color-sense  allowed  to  continue  in  service,  to  find 
if  they  are  better,  or  worse ;  and  these  periodical  examina- 
tions are  necessary  as  long  as  any  with  but  imperfect  color- 
sense  are  retained,  and  the  question  remains  undecided 
whether  their  defect  on  the  one  Hand  may  improve  or  be 
cured,  or,  on  the  other,  become  worse  or  develop  later." 

"  To  settle  positively  these  questions,  periodical  examina- 
tions must  be  made,  1st,  of  all  with  defective  color-sense, 
once  so  proved  ;  2d,  of  those  who  have  been  injui*ed ;  3d, 
of  the  whole  personnel,  in  order  to  detect  any  who  have 
become  color-blind  without  perceptible  cause.  How  far 
these  periodic  tests  should  be  carried  out  depends,  of  course, 
on  how  thoroughly  the  original  examination  has  been,  and 
how  strict  our  laws  of  rejection  have  been." 

"  From  what  has  been  said,  we  see  the  absolute  necessity 
of  the  government  and  railroad  administration  being  thor- 
oughly acquainted  with  the  color-sense  of  their  employes, 
and  the  thorough  testing  and  elimination  of  all  color-blind, 
as  also  the  preventing  the  admission  of  any  such  here- 
after into  service.  Whatever  stand-point  is  taken,  there 
rests  the  very  serious  importance  of  the  strictest  examina- 
tion of  the  entire  personnel.  To  carry  such  out  with  success, 
it  is  of  course,  first  of  all,  necessary  to  have  a  practical 
.uethod  of  testing  that  fulfils  its  purpose  in  every  possible 
direction.  We  lay  all  the  more  stress  on  this  point,  since 
we  believe  that  it  has  been  principally  the  want  of  such  a 
method  of  testing  which  has  hitherto  prevented  the  reform 
desired  and  urged  by  us." 


182  COLOR-BLINDNESS 


CHAPTER  XVIII. 

METHODS   OF  TESTING  FOR   COLOR-BLINDNESS. 

Trusting  that  by  this  time  my  readers  are 
convinced  of  the  necessity  of  testing  all  railroad 
employes  and  the  marine  personnel^  we  can  now 
turn  to  the  question  of  the  test  itself.  On  this,  of 
course,  depends  our  certainty  in  detecting  and  elim- 
inating the  color-blind.  The  whole  recent  wide- 
spread control  of  the  chromatic  defect  on  land  and 
sea  in  Europe  has  come  undoubtedly  from  Professor 
Holmgren  having  introduced  a  test  for  color-blind- 
ness, so  simple,  so  perfect,  and  so  applicable  to  the 
desired  purpose,  as  to  render  its  use  imperative, 
and  its  success  a  matter  of  necessity.  My  readers, 
I  think,  will  understand  the  subject  better  from 
hearing  what  he  has  to  say,  as  they  have  already 
seen  from  my  numerous  quotations  from  him.  As 
professor  of  physiolog}^  and  from  an  extended  ac- 
quaintance with  the  color-blind  and  great  experi- 
ence in  testing  for  the  defect,  just  what  he  has  to 
say  in  his  recent  work  as  to  methods  is  here  most 
valuable.  And  I  introduce  it  all  the  more  wil- 
lingly, as  my  own  personal  experience  as  well  as 
that  of  many  others  entirely  convinces  me  of  his 


ITS   DANGERS   AND   ITS   DETECTION.  183 

correctness,  shrewdness,  and  practical  knowledge. 
He  says,  — 

"  It  has  been  shown  that  color-blindness,  different  as  it  is 
from  the  normal  color-sense,  cannot  so  readily  be  detected  as 
might  be  supposed.  We  must,  in  fact,  regard  it  as  one  of 
the  peculiarities  of  the  defect,  resulting  from  conditions 
already  discussed,  that  it  so  often  escapes  detection. 

"  As  the  true  nature  of  color-blindness  became  known,  and 
the  peculiarities  of  the  persons  so  afflicted  recognized,  va- 
rious methods  were  devised  for  its  diagnosis.  There  are 
already  several  which  vary  either  in  the  principle  on  which 
they  are  based,  or  in  the  application  of  that  principle 
These  are  two  important  points,  and  any  error  affecting 
eithei  of  them  must  necessarily  lead  to  a  false  deduction. 
Moreover,  if  a  method  fulfils  both  of  these  calls  upon  it, 
yet  it  must  also  have  still  other  qualities,  such  as  we  may 
fairly  require  of  any  practical  means  of  examination  which 
is  to  assist  us  to  our  desired  end.  It  must,  namely,  be 
reliable,  and  of  quick  and  ready  application. 

"  The  great  majority  of  people  are  inclined  to  believe 
that  the  best  method  of  testing  the  railroad  personnel  for 
color-blindness  would  be  the  use  of  the  signals  employed,  — 
namely,  the  lanterns  and  flags,  —  as  being  the  most  direct, 
easiest,  and  suitable.  This,  to  every  practical  man  w^ho  has 
made  no  special  study  of  color-blindness,  is  so  obvious  as  to 
be  a  recognized  fact.  Any  control  which  w^e  are  here  con- 
cerned with  has  only  the  aim  of  preventing  the  mistaking 
the  signals  by  the  responsible  personnel.  What  more  simple, 
is  asked  with  seeming  right,  than  to  be  assured  that  the 
railroad  employes  can  distinguish  the  signals  ?  What  other 
method  can  quicker  bring  us  to  our  desired  end?  and  how 
can  we  reach  it  more  readily,  since  these  signals  are  in  use 
on  all  railroads?  At  first  sight  it  would  seem  as  if  there 
was  no  answer  to  this,  and  that  we  must  regard  any  control 
as  sufficient  wdiich  proved  that  all  the  personnel  could  dis- 
tinguish the  colors  of  the  signals.  But  there  is  another 
condition  necessary.  The  examination  must  not  only  prove 
that  the  men  are  able  to  distinguish  one,  two,  or  any  definite 
number  of  lanterns  and  flags,  so  or  so  often,  but  that  they 
can  distinguish  all  flags  and  all  lanterns  under  every  condi- 


184  COLOR-BLTNDNESS  : 

tion  ;  in  a  word,  that  their  color-sense  is  as  normal  as  we 
have  a  right  to  demand.  "We  do  not  deny  that  any  one 
thoroughly  familiar  with  color-blindness  and  its  practical  de- 
tection may  successfully  use  this  method  with  the  lanterns ; 
but  it  is  tedious,  inconvenient,  and  of  itself  gives  no  certain 
result.  Paradoxical  as  this  may  sound,  we  shall  have  to  con- 
fess that  such  a  method  is  inadmissible,  from  many  well- 
grounded  reasons.  It  is  therefore  our  duty  to  substantiate 
this  objection,  especially  as  this  method  seemingly  answers 
its  purpose,  whilst  in  reality  it  quite  defeats  it. 

"  The  railroad  signal-colors  ordered  are  red  and  green, 
without  special  nuances  of  the  colors  being  designated.  This 
latter,  fortunately,  is  not  insisted  on,  as  the  railroad  managers 
could  not  comply  with  it,  since  the  colors  vary  in  shade,  or 
nuance,  from  many  causes.  It  will  be  conceded  that  the  per- 
sonnel must  be  able  to  distinguish,  not  only  the  most  com- 
monly used  shades,  but  they  also  should  be  able  to  clearly 
see  red  and  green  colors  in  general.  This  is  not  difficult  for 
the  normal-eyed,  but  simply  impossible  for  the  color-blind. 
It  may  be  proved  by  testing  the  color-blind  with  selected 
lanterns ;  but  even  then  the  method  will  be  found  very  in- 
convenient. The  color-blind,  as  has  been  shown,  acquire 
from  practice  a  peculiar  capacity  for  distinguishing  colored 
signals.  How  and  what  this  is  has  been  explained,  and  that 
their  seeing  the  colored  signals  is  based  only  on  conjec- 
ture. Testing,  therefore,  with  lanterns  becomes  but  a  hazard 
between  the  examiner  and  examined,  where  the  latter  may 
readily  often  win,  and  where  the  former  bears  all  the  loss  if 
the  examined  afterwards  fails  but  once.  Of  course  the  ex- 
aminer is  sure  to  win  if  the  play  is  continued  long  enough ; 
for,  if  we  know  beforehand  the  examined  is  color-blind,  we 
can,  sooner  or  later,  cause  him  to  make  a  mistake  as  to  the 
color  of  the  lanterns.  But  if  we  do  not  know  that  he  is 
color-blind,  and  are  testing  him  to  decide  this,  then  we  shall 
soon  find  how  unadapted  this  method  is,  and  how  unpractical. 
Naturally  much  depends  upon  just  how  it  is  employed.  For 
instance,  let  us  suppose  that  the  usual  colored  lights  are 
shown  to  the  examined,  one  after  the  other,  and  he  is  asked 
their  color  or  meaning,  whilst  from  his  answer  his  color-sense 
is  to  be  decided  on.  Now,  as  we  have  already  shown,  the 
iolor-blind  may  decide  rightly;  but  we  need  hardly  add  that 


ITS    DANGERS    AND   ITS    DETECTION.  185 

the  normal-eyed  may  fail  from  carelessness,  inattention,  or 
even  from  lapsus  linguce.  Hence  a  color-blind  is  passed  as 
normal,  and  the  reverse :  so  in  this  form  the  method  is  not 
practical.  To  attain  certainty  the  test  must  be  continued, 
and  repeated  till  the  examined's  color-sense  admits  of  no 
doubt.  But  how  often  must  we  repeat  in  order  to  be  sure? 
How  often  must  mistakes  be  made  to  prove  color-blindness? 
or  how  often  may  they  be  made,  and  the  defect  still  be  con- 
sidered not  present  ?  It  is  of  course  impossible  to  decide 
these  questions.  Certainty  naturally  increases  with  the 
number  of  trials  :  but  the  method  is  still  untrustworthy ;  and 
it  is  depending  too  much  on  the  knowledge  and  experience 
of  the  examiner  in  reference  to  color-blindness  to  expect  a 
decision  from  him  based  on  such  tests.  This  method  of  test- 
ing with  railroad-lanterns  takes,  of  course,  even  if  supposed 
sure,  a  great  deal  of  time,  and  therefore  is  inconvenient  and 
unpractical  in  the  examination  of  hundreds  of  persons  at 
once.  The  method  is  also  inconvenient  as,  from  the  princi- 
ple it  involves,  —  namely,  the  detecting  the  color-sense  of  the 
persomiel  by  the  objects  their  duty  requires  them  to  recog- 
nize, —  the  test  must  be  made  on  the  railroad  itself.  A  prac- 
tical method  of  testing,  however,  should  be  one  capable  of 
being  used  in  any  x^lace. 

"We  have  therefore  concluded  that  testing  for  color- 
blindness by  railroad-lanterns  is  for  many  reasons  impracti- 
cable, and  to  be  discarded.  It  is  worse  with  the  flags : 
attempting  to  use  them  would  cause  the  examining  surgeon 
to  overlook  the  majority  of  color-blind  employes.  After 
what  has  been  said,  it  is  not  necessary  to  discuss  this  fur- 
ther. We  admit,  of  course,  that  the  method  will  succeed 
better  in  testing  those  about  to  enter  the  service,  and  as  yet 
unfamiliar  with  the  signals  :  but,  if  such  an  examination  re- 
sulted unfavorably,  there  would  be  no  just  ground  to  refuse 
the  applicant  if  it  is  believed  that  color-blindness  is  curable; 
and  we  do  not  clearly  recognize  the  distinction  between  cor- 
rectly seeing  the  colors  and  correctly  naming  them.  We  can 
give  no  better  advice  to  those  who  are  not  convinced  of  the 
truthfulness  of  this,  than  to  try  it  themselves.  They  will 
soon  find,  that,  for  testing  a  person  for  the  first  time,  lan- 
terns and  flags  are  useless. 

"  We  grant,  on  the  other  hand,  that  testing  with  colored 


186  COLOE-BLINDNESS  : 

lights  is  quite  practicable  when  we  want  to  examine  em- 
ployes already  found  somewhat  deficient,  and  desire  to 
decide  whether  they  can  remain  in  service  or  not.  In  this 
case  it  is  much  better,  instead  of  the  usual  colored  lan- 
terns, to  have  a  large  number  of  colored  glasses  which 
can  be  placed  before  the  light,  or  lanterns  of  varying  shades 
of  color.  Then  any  one  who  will  work  methodically  will 
convince  himself  and  others  that  the  views  we  have  ex- 
pressed and  defended  as  to  color-blindness  are  correct ;  and, 
as  to  less  faulty  chromatic  sense,  its  true  effect  in  recogni- 
tion of  the  signals  will  be  duly  appreciated.  For  instance, 
persons  with  feeble  color-sense,  to  distinguish  small  colored 
surfaces,  must  come  much  nearer  to  them  than  the  noimal- 
eyed  ;  whilst  those  who  are  completely  color-blind  cannot 
tell  the  ordinary  lights  with  certainty,  even  when  close  to 
them.  Many  color-blind  are  even  unable  to  say  there  is  a 
light,  when  very  feeble,  behind  a  dark-red  glass.  A  very 
definite  result  is  obtained  by  letting  two  color-blind  signal 
each  other  with  lanterns  I  have  had  specially  constructed. 
They  then  make  the  most  marked  mistakes.  This  is  a  very 
good  plan  to  convince  a  sceptical  railroad  official,  as  well  as 
the  color-blind  themselves.  From  the  result  of  our  investi- 
gations, we  deduce  the  following  as  applicable  to  every  test 
of  color-blindness  :  the  examination  is  not  to  ascertain  the 
relation  of  color-sense  to  certain  signals,  whatever  these 
latter  may  be,  but  to  decide  plainly  and  surely  whether  a 
given  person  is  color-blind  or  not,  or  whether  the  color-sense 
is  deficient  or  normal. 

"  The  test  is  to  find  out  the  character  of  the  color-blind- 
ness, not  by  ascertaining  all  its  peculiarities,  but  simply  one 
or  more,  which  quite  serves  our  purpose.  This  is  all  needed, 
and  only  exceptional  cases  require  further  examination. 
Now,  there  are  a  number  of  methods  which  combine  more  or 
less  the  essential  characters  we  need  in  a  practical  test. 
Without  discussing  them  all,  we  will  here  notice  only  a  few 
points  which  will  enable  us  to  apply  some  rules  to  govern 
our  decision  as  to  which  means  of  examination  to  employ. 
There  is  hardly  any  which  could  not  be  used,  and,  if  we 
could  carry  it  out  with  the  necessary  knowledge,  would  not 
serve  our  purpose  as  a  method  of  control,  at  least  when 
repeated  trials  could  be  made.     On  the  other  hand,  there 


ITS   DANGEES    AXD   ITS   DETECTION.  187 

are  methods  ^vhich,  used  alone,  would  never,  or  but  seldom, 
give  us  positive  results,  or  which  are  so  tedious  and  incon- 
venient as  to  be  quite  unpractical.  To  this  class  must  be 
referred  all  those  which,  like  the  test  with  the  lanterns,  let 
the  examined  look  at  various  colors  or  colored  objects,  and 
then  demand  of  them  their  names. 

"  This  decision  is  based  on  what  we  have  already  ex- 
pressed, and  also  upon  our  own  experience  in  reference  to 
the  way  and  manner  in  which  the  color-blind  learn  the 
names  of  colors,  and  the  success  practice  gives  them.  But 
we  do  not  want  to  learn  the  degree  of  skill  a  person  can  at- 
tain in  naming  colors,  but  how  he  sees  them;  in  other  words, 
the  character  of  his  color-blindness.  The  great  difference 
between  these  two  powers  cannot  be  too  well  recognized,  and 
on  this  ground  alone  we  must  again  recur  to  the  subject. 
Just  how  a  color-blind  sees  a  color  it  is  not  possible  to 
decide  ;  for  it  is  a  subjective  sensation.  On  the  other  hand, 
we  may  form  an  opinion  as  to  the  character  of  his  color-sense 
by  the  confusion  or  the  mistakes  which  he  makes  in  putting 
colors  together,  which,  to  the  normal-eyed,  are  essentially 
different.  Hence  any  method,  to  answer  all  demands  upon 
it,  must  be  based  upon  the  comparison  between  different  col- 
ors, and  the  confusion  the  coloi'-blind  make  in  this  compari- 
son. An  example  will  render  our  idea  more  clear,  and  show 
the  importance  of  it.  Suppose,  for  instance,  we  have  a  green- 
blind.  Xow,  experience  shows  that  such  a  one  confuses 
the  shades  of  three  colors,  which  are  very  different  to  the 
normal  eye ;  namely,  purplish  red,  green,  and  gray  :  or  he 
regards  them  as  exactly  similar.  Theory  shows  the  reason 
of  this  very  clearly.  The  green-blind  has  not  the  receptive 
or  percipient  organ  of  green.  Purple,  green,  and  gray  pass 
with  the  green-blind  for  really  one  and  the  same  color, 
which,  however,  from  what  he  hears,  receives  under  different 
circumstances  the  separate  names.  The  consequence  is,  that 
he  also  calls  this  color  sometimes  by  one  and  sometimes  by 
the  other  name,  or  always  calls  it  by  one  and  the  same 
name,  —  often  by  the  name  he  first  attached  to  it,  or  most 
often  hears.  If  we  test  such  a  person  by  letting  him  name 
the  colors,  then,  in  accordance  with  the  theory,  the  character- 
istic signs  of  green-blindness  must  in  turn,  and  after  many 
trials,  show  themselves.     Y/ithout  guidance  from  the  theory 


188  COLOR-BLINDNESS  : 

it  is  difficult  to  obtain  any  clear  and  correct  conception  of 
the  color-sense  of  a  green-blind.  If  he  uses  all  the  three 
names,  he  will  often  be  right,  and  as  often  wrong.  In  the 
first  case  he  will  readily  be  thought  normal-eyed,  and  in  the 
second  what  Goethe  said  will  certainly  occur,  — '  one  gets  into 
the  greatest  perplexity,  and  fairly  dreads  becoming  crazy.' 
If  the  green-blind  carefully  uses  but  one  of  the  names,  it 
will  be  one  of  the  three,  '  purple  '  (falsely  called  '  red '), 
'green,'  or  'gray,'  which  he  applies  to  all.  Suppose  now  he 
uses  the  name  'green  : '  then,  according  to  a  method  depend- 
ing on  the  naming  of  colors,  we  should  conclude  that  he  sees 
purple  and  gray  badly,  but  green  distinctly.  His  color-sense 
will  of  course  be  regarded  as  abnormal ;  but  no  one  would 
suppose  he  was  green-blind,  since  he  seems  to  see  that  color 
perfectly.  Yet  this  green-blind  will  be  regarded  as  such  if 
he  used  the  term  'red'  (purple)  or  'gray.'  We  trust  this 
example  will  remove  all  doubts  as  to  which  of  the  two  points 
of  view  is  the  correct  one.  Without  further  defending  it,  we 
hold  the  fact  proved,  that  any  practical  method  of  examina- 
tion must  be  based  on  the  principle  of  comparison" 

From  what  Professor  Holmgren  has  laid  down, 
we  can  readily  understand  why  certain  methods 
are  not  practical  as  well  as  not  scientific.  These 
methods  we  must  therefore  briefly  criticise  before 
explaining  his.  Let  us  first  remember  what  has 
been  said  as  to  any  method  which  calls  upon  the 
examined  to  name  colors  shown  them,  —  to  those 
unacquainted  with  color-blindness,  apparently,  the 
simplest  and  most  suggestive.  To  all  such  meth- 
ods we  may  apply  Professor  Helmholtz's  criticism : 
"  As  to  the  examination  of  the  color-blind,  simply 
asking  them  to  name  this  or  that  color  will  natu- 
rally elicit  but  very  little." 

Several  ways  of  employing  "  simultaneous  con- 
trast "  have  been  proposed  and  carried  out.  Dr. 
Stilling  of  Cassel  used  colored  shadows.  If  we 
hold  before  a  lamp  a  piece  of  colored  glass,  and 


ITS   DANGEES   AND   ITS   DETECTION.  189 

allow  the  light  thus  colored  to  fall  upon  a  white 
screen,  this  will  then  appear  colored.  Now,  hold- 
ing a  pencil,  for  instance,  before  the  screen,  we 
shall  have  a  shadow  cast  on  the  colored  surface. 
This  shadow  will,  to  the  normal  eye,  appear  of 
the  complementary  color  of  the  glass  before  the 
lamp ;  whilst  to  the  color-blind  the  shadow  will 
appear  colorless  or  black  or  gray.  On  this  prin- 
ciple is  constructed  Dr.  Cohn's  chromasciopticon, 
as  also  the  chromatoscope  made  by  Waldstein. 
Such  tests  are  not  as  practical  even  as  they  sound, 
though  Stilling  showed  how  we  could  get  the 
colored  shadows  by  daylight.  I  would  refer  to 
Dr.  von  Reuss's  article  in  support  of  my  state- 
ments. Holmgren's  more  practical  use  of  the 
shadows  I  describe  below. 

Another  method  of  using  simultaneous  contrast 
is  based  on  the  experiment  of  Ragona-  Scina,  and 
carried  out  by  Colin  and  b}^  Pflliger.  If  we  bend 
a  piece  of  white  cardboard  to  a  right  angle,  and 
then  fasten  to  the  adjacent  surfaces  a  little  piece 
of  black  cloth,  we  can  hold  a  plate  of  colored  glass, 
with  one  edge  resting  in  the  angle  of  the  paper, 
about  dividing  the  right  angle  made  by  the  card- 
board :  now,  looking  down  from  above  through 
the  glass,  we  see  the  horizontally  placed  piece  of 
black  cloth  of  the  color  of  the  glass ;  but  we  shall 
also  see  the  reflection  of  the  vertically  placed  piece 
of  cloth,  and  this  will  appear  of  the  complement- 
ary color  of  the  glass.  These  do  not,  of  course, 
so  appear  to  the  color-blind. 

A  test,  based  on  H.  Meyer's  law  of  simultaneous 
contrast,  has  been  proposed  by  Weber  and  Pflii- 
ger.     This  is  well  given  in  the  English  translation 


190  COLOR-BLINDNESS  : 

of  "  Bezold's  Theory  of  Color,"  by  Mr.  Kohler. 
Black  letters  printed  on  colored  paper,  when  cov- 
ered with  thin  tissue  paper,  show  through  this  of 
the  complementary  color.  A  gray  stripe  on  a 
colored  ground,  when  gazed  at,  takes  the  comple- 
mentary color  of  the  ground. 

Any  other  methods  of  producing  simultaneous 
contrast  may  of  course  be  employed  ;  but  they  are 
useless,  as  requiring  of  the  examined  color-names. 

Successive  contrast,  or  complementary  after- 
images, has  been  suggested  by  Schirmer  and  by 
Cohn.  If  we  look  steadily  a  few  seconds  at  a  col- 
ored surface  on  a  gray  ground,  and  then  quickly 
remove  the  colored  surface,  the  ground  will  appear 
of  the*  complementary  color.  We  here  again  must 
depend  on  what  the  examined  say  they  see. 

A  method  of  testing  for  color-blindness  will  at 
once  suggest  itself  in  the  use  of  the  spectroscope. 
Hirschberg  has  recently  arranged  one  in  which  we 
have  two  spectra,  one  over  the  other,  but  in  re- 
versed order.  Movable  slits  allow  us  to  choose 
two  colors,  which  appear  just  alike.  The  mistakes 
of  the  color-blind  in  doing  this  show  their  defect. 
Stilling  proposed  the  use  of  the  spectra  of  certain 
metals,  —  natrium,  lithium,  thallium,  &c. ;  and  in- 
teresting results  have  been  thus  obtained. 

Rose's  color-measurer  should  be  here  also  men- 
tioned, and  Briicke's  schistoscope,  —  only  useful, 
however,  for  scientific  examinations. 

A  method  of  testing  has  been  proposed  by  For- 
ster's  perimeter.  This  is  used  by  ophthalmic 
surgeons  in  determining  loss  of  chromatic  sense 
over  certain  portions  of  the  retina.  Small  spots 
of  color  are  brought  up  from  the  circumference 


ITS   DANGERS   AND   ITS   DETECTION.         191 

towards  the  centre  of  the  field  of  vision,  and  we 
can  thus  map  out  the  chromatic  visual  field. 

In  1871  Professor  Holmgren  directed  attention 
to  what  he  called  the  quantitative  disturbances  of 
the  color-sense,  or  incomplete  color-blindness. 
Professor  Donders  of  Utrecht,  in  1875,  carried  out 
this  idea  in  a  method  of  testing  which  gave  us,  not 
only  the  fact  that  the  examined  was  color-blind, 
but  also  in  what  degree.  This  is  described  in  a 
subsequent  chapter  as  used  on  the  Holland  rail- 
roads. 

Drs.  Dor  and  Fa^Tre  have  modified  Donders's 
method;  and  the  former  published  lithographic 
plates  of  the  colored  disks,  of  definite  sizes,  on  a 
black  background.  For  this  there  is  great  diffi- 
culty in  obtaining  the  proper  printed  colors,  both 
as  to  uniformity,  purity,  and  saturation. 

Suggestions  of  Professor  Holmgren  have  been 
carried  out  by  Dr.  Stilling  in  a  method  of  testing 
for  color-blindness  which  has  the  advantage  of  not 
calling  upon  the  examined  to  name  colors.  In  ac- 
cordance with  the  now  well-known  laws  of  color- 
blindness, letters  are  "printed  in  colors  on  a  colored 
ground :  these  the  color-blind  fail  to  see,  as  there  is 
no  contrast  to  them  between  the  letters  and  the 
ground  color.  Dr.  Stilling  has,  in  his  more  recent 
editions  of  this  test,  very  ingeniously  overcome,  in 
a  great  degree,  certain  difficulties ;  but  there  are 
other  practical  ones  which  cannot  be  overcome. 
There  is  no  comparison  between  it  and  the  scien- 
tific simplicity  of  Holmgren's.  It  may  be  used  as 
an  additional  method  by  those  thoroughly  acquaint- 
ed with  color-blindness  theoretically,  and  practised 
ill  testing  for  it.     Experience  has  proved  this  to 


192  COLOR-BLINDNESS  : 

those  who  have  attempted  to  use  Stilling's  cards 
in  testhig  large  numbers,  and  uneducated  people. 

Mr.  J.  Clerk  Maxwell,  in  1855,  proposed  a  meth- 
od of  judging  of  the  chromatic  sense  by  colored 
disks  revolving  on  a  top.  They  were  so  arranged 
that  the  various  colors  could  be  combined  in  any 
proportion.  We  can  thus  let  a  person  compare 
colors,  and  prove  their  chromatic  defect  by  their 
variation  from  the  normal-eyed.  Landolt  proposed 
a  modification  for  the  quantitative  determination  of 
color-blindness.  In  1870  Dr.  Woinow  proposed  the 
use  of  a  revolving  disk,  the  inner  circle  of  which 
was  one-half  each  of  black  and  white,  giving  us 
gray  when  revolving.  Three  rings  outside  of  this 
were  composed  of  equal  parts  of  two  of  the  three 
primary  colors,  —  red,  green,  violet.  To  a  person 
blind  to  the  color  not  represented  in  one  of  the 
rings,  this  ring  will  appear  gray  for  reasons  I  have 
previously  given.  Later  he  modified  his  disk,  as 
he  accepted  four  primary  colors.  The  inner  ring 
is  now  to  be  red  and  violet  (or  blue)  ;  the  outer, 
green  and  violet  (or  blue)  ;  the  tliird  is  left  out. 
If  the  outer  appears  gray,  like  the  centre,  then  we 
have  green-blindness  ;  if  the  inner,  then  red-blind- 
ness ;  if  both,  then  red-green-blindness. 

More  than  forty  years  ago  Professor  Seebeck 
of  Germany  described  his  testing  a  number  of 
color-blind  by  methods  of  comparison  of  colors. 
He  used  some  two  hundred  pieces  of  colored 
paper,  and  allowed  the  examined  to  sort  these, 
putting  together  wdiat  looked  to  them  alike.  This 
was  the  first  time  a  true  method  was  used ;  and 
he  obtained  very  valuable  results,  having  shown 
that  there  were  different  kinds  of  color-blindness, 


ITS   DAXGEES   AND  ITS   DETECTION.         193 

and  different  degrees  of  each  kind, — a  most  im- 
portant fact,  as  I  have  previously  described. 

In  1855  Professor  Wilson  of  Edinburgh  pub- 
lished the  first  monograph  in  book-form  on  color- 
blindness. In  testing  various  individuals  he  used 
little  bundles  of  colored  worsteds,  letting  them 
sort  them  out,  and  put  together  those  seeming 
alike.  The  principle  was  the  same  as  Seebeck's, 
and  a  true  one  of  comparison,  the  examined  not- 
being  obliged  to  name  any  colors.     He  says,  — 

"  Candidates  for  appointments  Tvhere  good  eyesight  is 
required  are  not  likely  to  exaggerate  their  defects  of  vision. 
Whenever,  therefore,  any  hesitation  in  distinguishing  colors 
is  manifested,  it  should  be  further  tried  by  giving  the 
party  under  examination  parcels  of  differently  colored  cloth, 
paper,  glass,  and  the  like,  and  requesting  him  to  assort 
them  according  to  their  colors.  Reds,  greens,  browns,  and 
lilacs  should  form  an  essential  part  of  these  parcels,  but  not 
to  the  exclusion  of  other  tints  and  shades.  Xo  person 
markedly  color-blind  vrill,  I  am  persuaded,  escape  detection 
if  tried  in  this  way ;  and  the  kind  and  number  of  mistakes 
which  he  commits  will  measure  the  extent  of  his  color- 
blindness. The  mode  of  examination  thus  explained  is 
within  the  reach  of  railway  superintendents  and  shipmasters, 
and  will  serve  every  practical  end.  But  where  railway 
servants,  sailors,  soldiers,  or  others,  undergo  preliminary 
examination  by  a  surgeon,  a  more  minute  examination 
might  be  made,  and  in  another  way." 

He  refers  to  the  colored  disks,  spun  on  a  top,  of 
Maxwell.  I  quote  from  Professor  Wilson  to  show, 
first,  that,  though  he  used  comparison  tests,  yet 
he  did  not  seemingly  recognize  that  such  alone 
were  of  value,  as  proved  by  what  he  suggests. 
Had  the  Young-Helmholtz  theory  of  color-percep- 
tion been  then  as  thoroughly  disseminated  as  now, 
he  would  no  doubt  have  appreciated  its  value  in 


194  COLOR-BLINDNESS  : 

explaining  color-blindness.  It  was  not  so  applied 
till  1875  by  Professor  Holmgren,  who  at  the  time 
was  unaware  of  Wilson's  results. 

The  Young-Helmholtz  theory  of  color-percep- 
tion suggested  to  Professor  Holmgren  the  value 
of  sorting  worsteds  in  a  certain  way,  based  upon 
the  application  of  this  theory  to  the  vision  of  the 
color-blind.  This  method  of  his,  and  the  manner 
of  using  it,  I  shall  give  in  extenso  and  in  his  own 
words,  and  therefore  will  here  only  speak  of  some 
other  tests  which  have  been  copied  from  it. 

Dr.  Daae  of  Kragero,  Norway,  has  had  little 
squares  of  worsted  worked  on  a  card  in  rows. 
Some  rows  are  correct;  namely,  arranged  from 
the  darker  to  lighter  of  the  same  color.  Others 
are  arranged  of  the  colors  the  color-blind  especially 
confound ;  and  they  will  say,  when  asked,  that 
these  rows  are  correct.  The  card  is  very  con- 
venient, not  larger  than  an  octavo  volume,  and 
the  colors  arranged  to  detect  red,  green,  or  violet 
blindness. 

Dr.  Cohn  of  Breslau  proposed  working  worsted 
letters  on  a  ground  such  as  the  color  of  the  letter 
is  usually  confounded  with  by  the  color-blind. 
These  are  very  deceptive  to  the  color-blind,  and 
they  wonder  at  the  normal-eyed's  assertion  that 
there  are  letters  on  the  worsted  surface.  But  the 
deception  is  only  perfect,  and  the  detection  sure, 
when  the  color  of  the  letters  and  the  ground-work 
are  just  suited  to  the  especial  kind  and  degree  of 
color-blindness  of  the  examined.  The  test  as  a 
modification  of  Holmgren's  has  no  advantage,  and 
is  not  very  practical. 

Dr.  Magnus  of  Breslau  has  lately  proposed  a 


ITS   DAXGEHS   AND   ITS   DETECTION.  195 

modification  of  Holmgren's  test  by  letting  the  ex- 
amined pick  out  from  bundles  of  colored  worsteds 
those  which  match  the  colors  of  the  solar  spec- 
trum shown  them  at  the  same  time.  This  can  be 
used  as  an  additional  method  by  examiners,  but  is 
not,  of  course,  as  convenient  and  practical  as 
Holmgren's  simple  plan. 

Professor  Bonders  has  recently  also  proposed 
and  used  an  arrangement  of  worsteds.  On  a  httle 
disk  of  wood  one  of  the  colors  is  wound ;  and  the 
other,  which  the  color-blind  cannot  distinguish 
from  the  first,  is  so  wound  over  it  as  to  form 
rays  or  a  star.  A  large  number  of  these  pairs 
are  chosen,  guided  by  the  selection  various  color- 
blind make  with  Holmgren's  test ;  that  is,  the 
two  worsteds  on  the  disk  are  such  as  the  color- 
blind say  look  to  them  quite  alike.  A  color-blind 
is  therefore  detected  in  not  being  able  to  select 
those  which  to  the  normal-eye  present  contrasting 
colors. 

I  have  thus  given  Holmgren's  discussion  of  the 
principles  of  a  correct,  scientific,  and  sure  test  for 
the  detection  of  color-blindness,  and  briefly  ex- 
plained what  tests  have  been  proposed,  because 
the  whole  subject  is  new  to  us  in  the  United 
States,  and  the  future  control  of  color-blindness, 
and  assured  safety  from  its  dangers  thereby  ac- 
quired, so  greatly  depend  upon  the  emploj'ment 
of  an  absolutely  certain  method,  thorouglily  and 
understandingly,  by  competent  examiners. 


196  COLOE-BLINDNESS  : 


CHAPTER  XIX. 

Holmgren's   method  of    testing.  —  examina- 
tion AND  DIAGNOSIS. 

Justice  to  Professor  Holmgren  demands  that  I 
should  here  explain  what  he  has  done  in  reference 
to  these  various  forms  or  methods  of  testing  for 
color-blindness,  and  the  study  of  color-sense.  He 
has  been  over  the  whole  subject  before  the  recent 
observers  I  have  mentioned,  who  have  attached 
their  names  to  this  or  that  special  modification. 
His  method  of  examination  with  the  worsteds  — 
to  be  given  in  his  own  words  in  this  chapter  —  is 
therefore  to  be  considered  as  a  natural  develop- 
ment of  his  special  studies. 

March  31,  1871,  he  published  his  views  on 
"  Color-Blindness  and  the  Young-Helmholtz  Theory 
of  Color."  ^  He  there  discussed  this  theory,  and 
the  methods  heretofore  used  in  testing  color-blind- 
ness. He  also  gave  the  explanation  of  the  peri- 
metric examinations  afterwards  carried  out  by  him. 
By  experiments  with  Maxwell's  rotating  disk  he 
found  the  true  difference  between  red  and  green 

1  Om  Faxgblindhet  och  den  Young-Helmholtz'ska  Fargtheo- 
rien,  1871. 


ITS   DANGERS   AKD   ITS   DETECTION.  197 

blindness,  explaining  seven  cases  of  complete  color- 
blindness,—  five  red  and  two  green.  He  seems 
to  have  first  shown  that  green-blindness,  as  a  dis- 
tinct form,  in  conformity  with  Young's  hypothesis, 
did  exist,  and  proved  it  by  exact  experiments.  In 
this,  time  has  shown  him  to  be  correct. 

Nov.  3, 1871,  he  published  "  On  Forster's  Perime- 
ter and  the  Topography  of  the  Color-Sense."  ^  This 
contains  a  description  of  the  perimetric  examina- 
tions and  the  results  thereby  obtained,  especially 
the  three  separate  zones  of  the  field  of  vision  of 
Woinow,  in  relation  to  color-perception. 

He  used  the  point  of  fixation  as  the  centre  —  the 
physiological  centre  —  in  contradistinction  to  the 
blind  spot,  —  the  pathological  centre  as  he  terms  it. 
He  here  describes  a  series  of  perimetric  examina- 
tions of  the  color-blind,  beginning  with  the  normal 
color-sense,  and  following  up  to  complete  color- 
blindness. He  also  first  gives  here  a  description 
of  what  he  called  incomplete  or  partial^color-blind- 
ness.  This  is  important  to  notice,  as  Stilling 
attributes  wholly  to  Donders  our  knowledge  and 
understanding  of  this  form  of  chromatic  defect; 
whereas  Holmgren  had  very  clearly  defined  it  as 
a  quantitative  disturbance  of  the  color-sense. 

Incomplete  or  partial  color-blindness, — espe- 
cially incomplete  red-blindness,  —  he  shows,  is 
characterized  by  two  principal  points:  First,  in 
indirect  vision  with  the  perimetric  examination, 
the  field  of  vision  differs  from  that  of  the  complete 
color-blind  by  having  a  normal  central  field ;  but 
it  is  unlike  the  normal  color-sense  in  having  a 
much   smaller   central   field,  thus   in   both   ways 

1  Om  Forsters  Perimeter  och  Fargsinnets  Topograph!,  1871. 


198  COLOR-BLINDNESS  : 

being  only  a  quantitative  difference.  Second,  in 
direct  vision  at  the  point  of  fixation,  partial  color- 
blindness differs  from  complete ;  thus,  with  good 
illumination,  sufficiently  large  colored  surfaces  can, 
at  short  distances  and  with  careful  fixation,  be 
correctly  distinguished  in  the  sense  of  the  normal- 
eyed.  It  is  different  from  the  normal,  however, 
in  that  the  discernment  of  colors  is  uncertain,  and 
resembles  the  complete  red-blind  when  the  light  is 
poor,  the  distance  considerable,  or  the  object  small, 
or  when  indirect  vision  is  called  upon  to  assist. 
Now,  these  points  have  been  scientifically  carried 
out  and  formulated  by  Professor  Donders  since 
then ;  but  they  were  understood  and  described  in 
principle  by  Holmgren  as  early  as  1871. 

From  his  pernnetric  examinations  he  concluded 
that  the  three  color-perceptive  elements  have  from 
the  centre  outwards  different  extensions,  so  that 
they  all  three  occupy  the  central  field;  whilst  in 
the  middle  •  zone  only  green  and  violet  perceptive 
elements  exist,  and  in  the  outer  zone  only  one  of 
the  latter  two.  This  he  thought  to  be  the  green, 
as  most  peripheric ;  but  subsequent  examinations 
proved  it  to  be  the  violet. 

He  also  in  this  article  expressed  the  belief  that 
the  property  of  a  specific  sensation  for  green  in 
any  degree  is  inseparable  from  the  property  of  the 
sensation  for  red.  This  afterwards  became  the 
basis  of  Hering's  theor}^ 

Oct.  31,  1873,  he  published  "  On  Theories  of 
Color-Blindness."  ^  This  is  a  continuation  of  his 
previous  work  giving  his  theoretical  ideas.  It 
criticises  Fick's  theory,  and  endeavors  to  reconcile 

1  Om  Fargblindhetens  Theori,  Oct.  31, 1873. 


ITS   DANGERS   AND   ITS   DETECTION.  199 

the  facts  SO  far  established  with  Young's  theory 
of  color.  The  difference  between  Fick's  views 
and  Holmgren's  is,  that  the  former  refers  the  ma- 
terial process  of  color-perception  to  the  peripheric 
retinal  elements,  whilst  the  latter  would  equally 
divide  it  between  these  elements  and  the  central 
apparatus  in  the  brain.  He  also  criticises  R.  Schir- 
mer's  article  on  congenital  and  acquired  anomalies 
of  color-perception,  in  which  Schirmer  gives  a 
series  of  pigment  colors  which  have  eccentric  fields 
of  vision  of  varying  size.  He  holds,  that,  in  ex- 
amining: the  central  as  well  as  the  eccentric  field 
of  vision,  the  proper  selection  of  the  grades  of 
color  has  been  neglected.  He  gives,  therefore,  an 
idea  of  those  which  are  equivalent ;  that  is,  pig- 
ments which,  ceteris  paribus^  correspond  to  the 
same  visual  fields,  and  are  recognized  at  the  same 
distance  from  the  point  of  fixation. 

Holmgren  also  gives  some  cases  of  complete 
green-blindness,  the  characteristics  of  which  are 
especially  shown  in  this  article.  There  are,  be- 
sides, some  improved  methods  of  carrying  out  the 
perimetric  examinations  described. 

In  1874  Professor  Holmgren  published  an  article 
"On  the  Theory  and  Diagnosis  of  Color-Blind- 
aess."  ^  This  contains  the  theoretical  and  practi- 
cal groundwork  for  his  method  of  detecting  color- 
blindness, since  published  and  given  here  in  full. 
He  develops  it  theoretically  from  the  Young- 
Helmholtz  theory,  and  practically  from  Seebeck's 
method.  He  published  a  plate  with  colored  let- 
ters, in  this  article,  on  the  same  principle.     He  also 

1  Om  den  Medfodda  Fargblindhetens  Diagnostik  och  Teori. 
Nord.  Med.  ArMv.,  B.  vi.  No.  24-28. 


200  COLOB-BLmDNESS  : 

then  warned  against  the  misuse  of  the  table,  and 
took  the  same  position  which  he  now  holds  in 
reference  to  all  such  arrangements  of  material, 
and  in  defence  against  imitators.  This  plate  of 
colored  letters  clearly  shows  it  was  the  basis  on 
which  so  much  invention  has  been  since  made. 

He  also  further  discussed  the  true  subjective 
color-sense  of  the  color-blind.  He  proposed  means 
for  rendering  the  color-perception  of  the  normal- 
eyed  like  that  of  the  color-blind,  so  that  they 
would  see  colors  like  the  latter.  This  he  accom- 
plished with  colored  glasses  and  colored  solutions, 
as  has  since  been  done  by  Delboeuf,  as  described  in 
a  previous  chapter. 

Returning  to  the  two  commonest  forms,  — 
namely,  red-blindness  and  green-blindness,  —  he 
gives  further  proof  of  the  existence  of  the  latter 
as  a  distinct  and  independent  form,  analyzing 
three  additional  cases  of  complete  green-blindness. 

Finally,  he  treats  the  question  of  the  color- 
visual  field  of  the  color-blind,  proving  that  they 
have  as  many  distinct  visual  fields  as  primary 
colors.  He  gives  in  two  plates  colored  perimetric 
visual  fields  of  the  color-blind. 

The  method  of  testing  as  developed  from  his 
investigations  I  will  now  present  as  originally 
given  by  him.  The  description  may  seem  unne- 
cessarily extended,  and,  to  the  general  reader, 
quite  uninteresting.  It  is,  however,  for  the  benefit 
of  those  who  are  in  the  future  to  examine  em- 
^^loyes  in  this  country.  Experience  with  testing 
for  color-blindness  will  prove  its  value,  and  the 
necessity  for  its  seeming  minuteness.  Neglect  of 
?ts  study  and  directions  has  given  rise  to  much 


ITS   DANGERS   A^B   ITS   DETECTION.  201 

confusion  and  waste    of  time    on   the   European 
roads,  the  proof  of  which  will  be  hereafter  given. 

PROFESSOR   Holmgren's   method  of  detectixg   color- 
blindness  AS   DESCRIBED  IN  HIS   ORIGINAL  WORK. 

"1.  — A  Short  Sketch  of  the  General  Principles  of  the  Method. 

"  Theoretically  our  method  most  resembles  those  of  See- 
beck  and  Maxwell,  as  it  is  based  upon  a  comparison  between 
different  colors.  It  therefore  first  seeks  to  discover  the 
chromatic  perception  of  the  subject,  disregarding  the  names 
he  gives  to  the  colors,  as  generally  it  is  not  necessary  he 
should  designate  the  names.  Our  method  resembles  See- 
beck's  most  in  this,  that  it  does  not  require  a  special  appa- 
ratus for  preparing  the  necessary  tints  for  the  examination: 
it  assumes  there  will  be  a  supply  of  objects  of  different 
colors  provided  in  advance.  It  agrees  again  with  this 
method  in  not  allowing,  as  Maxwell's  does,  the  person  ex- 
amined to  remain  passive,  and  simply  give  his  opinon  of  the 
resemblance  or  dissimilarity  of  the  shades  indicated,  but  re- 
quires him  to  discriminate  and  select  the  shades,  and  in 
consequence  reveal  by  an  act  the  nature  of  his  chromatic 
sense. 

"But  practically  our  method  differs  essentially  from  See- 
beck's.  His  certainly  gives,  in  a  certain  sense,  more  com- 
plete results  than  ours,  by  requiring  the  subject  to  thor- 
oughly classify,  in  accordance  with  their  reciprocal  resem- 
blances and  dissimilarites,  the  various  differently  colored 
objects  placed  before  him.  A  complete  table  of  his  whole 
system  of  colors  is  the  result  of  this.  Our  method,  on  the 
contrary,  requires  the  person  examined  to  select,  amongst  a 
large  number  of  variously-colored  objects,  those  alone  which 
resemble  the  sample  shown  him  by  the  examiner.  The 
difference  is  evident.  Seebeck's  method  is,  without  any 
doubt,  preferable  when  the  nature  of  the  color-blindness  in 
the  aggregate  is  to  be  considered ;  that  is,  so  long  as  this  is 
yet  unknown.  His  method  then  gives  a  more  complete  idea 
than  ours  of  the  nature  of  the  color-blindness.  But,  for  our 
actual  purpose,  the  main  question  is  to  discover  a  defect, 
with  the  entire  nature  of  which  we  are  acquainted  in  ad- 


20 2-  COLOR-BLINDNESS  : 

vance.  Our  practical  mission,  then,  is  evidently  to  discover, 
if  possible,  some  certain  sign  which  will  enable  us  to  accom- 
plish this  end  by  the  shortest  possible  route. 

"  If  a  single  proof  which  would  detect  the  color-blind  as 
certainly  as  if  he  revealed  to  us  his  entire  system  of  colors 
were  discovered,  this  would  undoubtedly  be  the  method  pre- 
ferred to  any  other,  as  it  w^ould  accomplish  the  object  much 
more  quickly  and  easily.  This  is  the  case  with  our  method: 
We  are  far  from  denying,  in  general,  the  value  of  a  thor- 
ough examination ;  but  we  will  say  that  it  may  sometimes  be 
superfluous.  Its  practical  advantage  will  not  be  very  great 
if  at  the  cost  of  a  great  loss  of  time ;  and  it  may  even  be 
prejudicial,  if,  under  a  multitude  of  details,  it  conceals  what 
is  essential,  —  in  a  word,  prevents  our  '  seeing  the  forest  on 
account  of  the  trees.'  All  this  may  be  applied  to  Seebeck's 
method,  when  the  object  in  view  is  the  one  of  which  we  are 
in  pursuit.  Our  method  again  endeavors  to  seize  as  rapidly 
as  possible  one  or  two  essential  characteristics  while  neglect- 
ing all  the  others.  A  single  caudal  feather  of  the  peacock 
reveals  whence  it  came;  a  single  flower  or  fruit,  the  plant 
whence  it  was  plucked ;  and  the  genus  man  is  recognized  if 
we  can  but  see  a  face.  It  is  only  wdien  the  face  is  muti- 
lated, the  flowers,  fruits,  and  caudal  feather  are  defective, 
that  in  certain  cases  it  is  necessary  to  have  recourse  to  other 
characteristics. 

"  Our  method  rests  upon  these  principles :  it  also  offers 
the  same  security  as  Seebeck's.  But,  as  regards  the  time 
necessary  to  accomplish  the  examination,  it  bears  nearly  the 
same  relation  to  that  of  the  learned  German  that  a  minute 
does  to  an  hour.  This  may  seem  a  very  trifling  matter  at 
the  first  glance,  but  is  in  reality  of  immense  practical  im- 
portance when  a  multitude  of  persons  are  to  be  successively 
examined.  A  simple  calculation  shows  us  in  fact  that  an 
examination  requiring  one  day  by  our  method  would  re- 
quire two  months  by  Seebeck's. 

"It  is  but  just  to  acknowledge  that  it  was  only  by  weigh- 
ing the  results  obtained  by  Seebeck's  method,  and  following 
the  Young-Iielmholtz  theory,  as  well  as  the  principles  we 
have  indicated  as  indisj^ensable  to  a  practical  method,  that 
we  have  succeeded  in  formulating  our  own  method,  such  as 
*ve  shall  explain  it  in  what  follows.     We  also  will  remark 


ITS   DAXGERS   AXD   ITS   DETECTION.  203 

that  it  is  very  simple,  and  easily  mastered ;  but  v^e  think 
this  is  likewise  often  the  case  with  all  that  is  useful  and 
practical,  and  that  simplicity  offers  great  advantages.  We 
prefer  this  method  because  it  seems  to  us  more  than  any 
other  to  fulfil  the  conditions  we  have  pointed  out  as  neces- 
sary to  a  practical  method ;  namely,  certainty,  rapidity,  and 
convenience.  The  only  inconvenience  of  any  moment,  be- 
sides those  it  has  in  common  with  a  greater  part  of  the 
others,  is,  that  it  requires  daylight.  It  can  undoubtedly  be 
used  by  artificial  light  (electrical  and  calcium  lights,  and 
certain  arrangements  of  lamp-lights  with  blue  glass);  but 
this  causes  much  loss  of  time. 

' '  After  this  rapid  sketch  of  the  general  principles  of  the 
method,  we  will  proceed  to  give  its  details,  and  shall  not 
fail  to  mention  generally  the  reasons  why,  amongst  several 
possibilities,  we  have  selected  this  or  that  process. 

"2.  —  The  Material  and  its  Arrangement. 

"  Our  method  demands  neither  costly  apparatus  nor  a 
special  place  for  the  examination.  The  only  necessary 
elements  are  a  number  of  variously  colored  objects.  It  con- 
sists in  taking  one  from  a  number  of  objects  promiscuously 
thrown  together,  and  asking  the  person  examined  to  select 
from  amongst  them  all  the  others  corresponding  with  the 
first  in  color.  With  regard  to  the  colored  objects,  it  of 
course  matters  little  in  principle  what  their  nature  is,  as,  in 
the  main,  the  method  never  changes,  no  matter  what  the 
kind  selected.  But,  practically,  the  choice  is  by  no  means 
a  matter  of  indifference.  Among  the  ordinary  objects  sug- 
gested, and  also  used  for  the  purpose,  are  pieces  of  colored 
paper,  glass,  or  silk,  or  Berlin  worsted,  &c.,  the  last  of  which 
teems  to  us  the  best,  for  the  following  reasons :  One  of  the 
chief  advantages  of  Berlin  worsted  is,  that  it  can  be  pro- 
cured in  all  possible  colors  corresponding  to  those  of  the 
spectrum,  and  each  in  all  its  shades  from  the  darkest  to  the 
lightest.  Such  selections  may  be  found  in  trade,  and  are 
easily  procured  when  and  where  desired.  It  can  be  used  at 
once,  and  without  any  jDreparation  for  the  examination,  just 
as  delivered  from  the  factory.  A  skein  of  Berlin  worsted 
is  equally  colored,  not  only  on  one  or  two  sides,  but  on  all, 


204  COLOR-BLINDNESS  : 

and  is  easily  detected  in  a  large  pile,  even  though  there  be 
but  one  thread  of  it.  Berlin  worsted  is  not  too  strongly 
glaring,  and  is,  moreover,  soft  and  manageable,  and  can  be 
handled,  packed,  and  transported  as  desired,  without  dam- 
age, and  is  conveniently  ready  for  use  whenever  needed. 

"  These  advantages  are  wanting  in  the  other  colored  ob- 
jects suggested  for  use.  Colored  paper  or  silk  may  be  used 
when  light  or  dark,  dull  or  bright  colors  are  wanted.  But 
they  both  have  these  inconveniences  :  they  must  first  be  cut 
into  suitable  pieces,  and  they  are  troublesome  to  handle. 
Moreover,  they  are  easily  concealed  from  view ;  and  it  is 
necessary  to  stretch  them  carefully  on  a  large  surface  to 
enable  them  to  be  seen  without  trouble.  They  are  often 
glaring.  They  reflect,  besides  their  particular  kinds  of  light, 
a  quantity  of  white  light,  which  is  a  prominent  defect,  as  it 
misleads  the  color-blind,  who,  as  we  know,  judge  of  colors 
by  the  intensity  of  light,  — that  is,  the  quantity  of  light ;  and 
he  consequently  estimates  differently  the  color  of  a  brilliant 
surface,  according  to  the  position  in  which  it  is  found  with 
regard  to  the  eye,  &c.  The  paper  is  often  colored  on  only 
one  side,  and  this  gives  rise  to  much  trouble,  as  it  is  neces- 
sary to  turn  the  pieces  from  one  side  to  the  other  to  see 
them  in  their  true  colors.  Finally,  from  being  so  much 
handled,  the  pieces  of  paper  or  silk  soon  become  tumbled 
and  faded. 

"  Colored  glass,  which  must  be  in  pieces,  is  not  suitable, 
from  the  fact  that  it  is  difficult  to  procure  it  in  sufficiently 
great  variety.  It  is,  besides,  troublesome  to  transport,  easily 
broken,  and  finally  inconvenient  for  using,  because  necessa- 
ry to  be  held  against  the  light  of  day,  or  a  luminous  source, 
in  order  that  the  color  may  be  seen.  The  advantage  of 
being  able  to  use  them  by  any  kind  of  light  does  not  coun- 
terbalance their  inconveniences.  , 

"  Although  these  are  not  all  the  objections,  the  preced- 
ing will  suffice  to  prove  the  advantages  of  Berlin  worsted. 
All  this  applies  equally  well  to  wafers,  powders,  colored 
solutions,  spools  of  colored  thread,  pieces  of  wood,  and  por- 
celain, especially  painted  for  the  purpose,  &c.  They  can  all 
be,  and  have  been,  employed;  but  none  of  these  objects  are, 
m  every  respect,  so  well  suited  to  our  purpose  as  Berlin 
worsted. 


ITS   DANGERS   AXD    ITS   DETECTION.  205 

"  A  selection  of  Berlin  worsted  is  then  made,  including 
red,  orang^e,  yellow,  yellow  green,  pure  green,  blue  green, 
blue,  violet,  purple,  pink,  brown,  gray,  several  shades  of 
each  color,  and  at  least  five  gradations  of  each  tint,  from  the 
deepest  to  the  lightest.  Green  and  gray,  several  kinds  each 
of  pink,  blue,  and  violet,  and  the  pale-gray  shades  of  brown, 
yellow,  red,  and  pink,  must  especially  be  well  represented, 

"  Ihe  choice  of  the  material  does  not  belong  specially  to 
our  method.  In  fact,  Seebeck  suggested  the  use  of  Berlin 
worsted,  which  was  employed  by  his  advice,  and  still  is  at 
present.  To  us  only  belongs  the  credit  of  originating  the 
manner  in  which  it  is  employed.  According  to  our  method, 
the  examiner  selects  from  the  collection  of  Berlin  worsted 
in  a  pile  on  a  convenient  table,  and  lays  aside  a  skein  of  the 
especial  color  desired  for  this  examination ;  then  he  requires 
the  one  examined  to  select  the  other  skeins  most  closely 
resembling  the  color  of  the  sample,  and  to  place  them  by  its 
side.  The  chromatic  sense  of  the  individual  is  decided  by 
the  manner  in  which  he  performs  this  task. 

"  The  result  of  comparison  which  the  examined  makes  — 
in  other  words,  the  little  skein  of  worsted  which  he  selects 
and  places  by  the  test — shows  us  in  reality  what  colors  seem 
alike  to  him,  and  thus  tells  us  his  relative  color-perception. 
The  rapidity  with  which  this  examination  is  made  does  not 
seem  to  directly  correspond  with  the  nature  of  the  chromatic 
sense,  but  to  depend  wholly  upon  the  character  of  the  person 
examined.  One  of  intelligence,  with  a  quick,  practical  mind, 
is  examined  in  less  than  a  minute.  In  this  time,  in  fact,  a 
normal  eye  could  easily  find  the  four  or  five  skeins  of  the 
same  color  as  the  sample,  and  the  color-blind  make  a  suffi- 
cient number  of  characteristic  mistakes  to  thoroughly  estab- 
lish the  diagnosis. 

"  It  might  be  supposed  that  this  method  could  be  further 
simplified,  and  time  thereby  saved,  by  previously  grouping 
the  colored  objects,  or,  in  other  words,  showing  to  the  exam- 
ined a  number  of  colored  objects  arranged  in  certain  system, 
and  asking  of  him  which  look  alike,  and  their  names.  Here 
the  worsteds  would  have  no  special  advantage  over  other 
colored  material,  and  could  be  replaced  by  objects  with 
bright  surfaces  not  necessarily  movable.  On  such  a  pro- 
posed table  the  various  colors  may  be  placed  without  any 


206  COLOR-BLINDNESS  : 

order,  or  in  a  definite  order  in  accordance  with  their  simi- 
larity. Thus  they  may  be  grouped  according  to, the  color- 
perception  of  the  normal-ejj-ed  or  the  color-blind,  and,  in  the 
latter  case,  in  different  groups  corresponding  to  the  different 
forms  of  color-blindness. 

"  The  grouping  of  colors  which  I  proposed  was  on  this  prin- 
ciple, and  it  is  printed  in  the  '  Nordst  Medicinskt  Arkiv.,' 
1874,  and  carried  out  in  the  plate  published  with  this 
book.  The  plan  is  a  good  one  where  we  are  dealing  with 
educated  and  intelligent  people,  and  many  color-blind  may 
be  thereby  detected.  To  be  at  all  complete,  and  generally 
practical,  this  method  must  have  a  much  larger  number  of 
shades.  Experience  shows  that  the  color-blind  is  often  un- 
certain as  to  the  similarity  between  two  colors,  depending 
less  upon  the  color  than  on  what  to  him  is  the  most  impor- 
tant distinguishing  mark ;  namely,  the  intensity  of  the  light, 
or  the  degree  of  saturation.  And,  as  to  equal  intensity  of 
two  colors  whose  similarity  he  would  find,  he  is  so  particular, 
that  the  test  may  be  just  too  much  or  too  little.  We  must 
add  that  all  color-blind  of  the  same  class  are  not  as  particular 
as  to  intensity  of  light  or  degree  of  saturation ;  and,  moreover, 
it  is  impossible,  on  plates  which  are  multiplied,  to  get  exact- 
ly the  necessary  colors,  whilst  the  price  increases  with  the 
number  of  colors.  The  difficulties  were  therefore  enough 
for  us  to  abandon  this  method.  The  worst  is,  however,  that 
the  supposed  gain  in  time  is  more  than  counterbalanced  by 
lack  of  conveniences  and  other  difficulties.  In  short,  the 
loss  is  greater  than  the  gain. 

"  These  remarks  hold  good,  not  only  in  reference  to  this 
form  of  test  proposed  by  me  in  1874,  but  also  to  all  colored 
tables  which  have  so  far  been  published.  A  proof  is,  the 
worked  worsteds  of  Dr.  Daae,  and  the  repeated  attempts  of 
Dr.  Stilling  to  construct  colored  plates.  As  is  known, 
neither  have  succeeded  in  solving  the  difficulties,  although 
careful  and  ingenious  attempts  have  been  made  to  conquer 
some  of  those  I  have  spoken  of.  These  tables,  from  the 
very  nature  of  the  subject,  can  only  have  a  limited  employ- 
ment as  an  additional  test,  but  are  for  the  examination  of 
masses  wholly  unserviceable.  Experience  has  perfectly 
proved  this  to  me,  and  will  the  same  to  every  expert.  The 
new  editions,  unfortunately,  are  not  changed  in  this  respect. 


ITS   DANGERS    AND    ITS    DETECTION.  207 

"  By  such  a  colored  plate,  or  any  similar  arrangement 
of  immovable  colored  objects,  the  very  -work  is  done  which 
should  have  been  by  the  examined ;  namely,  the  grouping 
of  colors  seemingly  alike.  If,  however,  this  is  not  done, 
and  the  colors  are  mixed  up,  then  we  cannot  let  them  be 
grouped  in  accordance  with  their  similarity.  The  value  of 
this  method  is,  that  the  objects  are  movable,  and  can  be 
mixed  and  sorted  anew. 

"  Careful  consideration  will  show  the  importance  of  this 
fact.  The  object  of  the  test  is  to  ascertain  a  subjective  sen- 
sation from  an  objective  expression.  Now,  man  has  but  one 
means  of  expressing  his  subjective  sensation  to  another ; 
namely,  by  muscular  action.  The  organs  of  speech  and  the 
limbs  are  the  apparatus  of  motion  best  answering  this  pur- 
pose, and  most  used  for  it.  Of  the  most  movable,  the 
tongue  and  hand  each  is  the  representative  of  its  group ;  and 
they  are  the  most  pliable  of  all  organs.  Both  equally  indi- 
cate the  different  actions  by  which  we  impart  our  thoughts 
to  others;  namely,  by  words  and  acts.  It  is  scarcely  neces- 
saiy  to  indicate,  that,  as  a  rule,  it  is  the  latter  (the  hands) 
which  we  rightly  have  greater  confidence  in  than  the  spoken 
word.  This  is  substantiated  in  testing  the  color-blind.  We 
have  seen  how  readily  they  are  detected  when  forced  to  act, 
whilst  we  must  equally  remember  that  the  names  they  give 
colors  are  often  exactly  adapted  to  conceal  their  defect.  If 
it  is  in  his  interest,  as  here  is  the  case,  not  to  expose  his 
defective  perception,  but  rather  to  conceal  it,  he  certainly 
can  do  this  better  by  speech  than  by  the  hands.  This  is  a 
general  law  applicable  here,  if  the  relations  between  the  per- 
ception and  denomination  of  an  object  are  recalled  as  we 
have  explained  them,  and  the  way  these  two  acts  are  com- 
bined in  education.  On  the  other  hand,  it  is  clear  that  our 
method  affords  the  opportunity,  in  connection  with  the  inves- 
tigation of  the  chromatic  sense,  of  learning  much  of  all  the 
peculiarities  relating  to  the  use  of  our  senses.  This  is  why 
we  maintain  the  principle  that  it  is  necessary  to  leave  to  the 
activity  of  the  hands  the  task  of  revealing  the  nature  of  the 
sensations,  and  to  have  recourse  to  the  tongue  only  for  veri- 
fication when  there  is  need  of  more  information. 

''The  combination  of  the  action  of  the  eye  and  hands, 
which  plays  in  general  so  important  a  part  in  the  training 


208  COLOR-BLINDNESS : 

and  use  of  the  senses,  is  also  of  great  consequence  in  this 
examination.  An  attentive  examiner,  especially  if  he  have 
already  acquired  some  experience,  can  draw  important  con- 
clusions from  the  manner  in  which  the  other  executes  his 
task,  not  only  and  directly  with  regard  to  the  nature  of  his 
chromatic  sense,  but  generally  as  to  his  intelligence  and 
character,  and  especially  in  some  cases  as  to  his  previous 
training  and  exercise  in  the  use  of  colors,  and  his  skill  in 
recognizing  them.  The  examination  affords  us  also  the 
opportunity  of  making  psychological  observations,  which 
contribute,  in  a  great  measure,  in  giving  us  a  clear  idea  of 
the  nature  of  the  chromatic  sense. 

"  A  practised  surgeon  can  often  detect  color-blindness  by 
the  first  gesture  of  the  examined,  and  make  his  diagnosis 
before  the  end  of  the  trial.  He  can,  according  to  the  man- 
ner in  which  the  task  is  performed,  form  a  judgment  of  a 
feeble  chromatic  sense  in  instances  which  are  proved  correct 
by  the  final  result.  He  also  can  and  must  see  whether  the 
result  is  erroneous  simply  on  account  of  a  misunderstanding 
or  a  want  of  intelligence,  just  as  he  can  see  whether  the 
really  color-blind  succeeds,  in  a  certain  degree,  from  much 
previous  exercise  or  a  considerable  amount  of  caution.  In 
short,  the  method  supplies  us  with  all  necessary  information ; 
so  that,  by  an  examination  made  with  its  assistance,  a  defec- 
tive chromatic  sense,  no  matter  of  what  kind  or  in  what 
degree,  cannot  escape  observation.  It  also  calls  upon  the 
examiner  to  watch  the  examined  very  carefully,  and  note 
his  every  motion.  Different  persons  act  very  differently, 
and  cause  the  surgeon  trouble  of  more  than  one  kind. 
People  of  medium  intelligence,  whether  they  are  color-blind 
or  not,  give  least  trouble,  provided  they  do  not  feel  called 
upon  to  be  too  shrewd.  The  examination  is  most  difficult 
with  people  of  small  intelligence,  or  of  feeble  and  unculti- 
vated color-perception,  or  when  we  have  a  color-blind 
already  tested  who  desires  to  escape  detection,  or  when  the 
examined  has  not  had  good  school-education.  Practical 
rules  for  these  special  cases  are  given  later. 

"The  principle  of  our  method  depends,  as  we  have  said, 
on  the  test  calling  for  the  selection  of  but  one  color  among 
many.  It  may  be  asked  what  need  of  such  a  number  of 
colors?     Would  not  a  smaller  answer  ?     We  reply  that  the 


ITS    DANGERS    AND    ITS    DETECTION.  209 

color-blind  avoids  detection  with  more  difficulty,  and  the 
diagnosis  hence  is  more  readily  made,  the  greater  the  num- 
ber of  the  various  colors.  The  normal-eyed  readily  selects 
the  right  ones  from  the  mass;  whilst  the  color-blind,  al- 
though the  right  ones  are  directly  before  him,  picks  out  the 
wrong  ones,  thereby  disclosing  the  character  of  his  defect. 
Therefore  the  greater  the  number  of  colors  the  better,  of 
course,  within  certain  limits. 

"  What  color  shall  we  take  for  our  sample  ?  This  is  of 
importance ;  for  we  must  of  course  decide  on  some  one 
color.  Experience,  as  well  as  the  Young-Helmholtz  theory, 
teaches  us  that  more  than  one  color  may  serve  as  the  sample 
in  searching  for  a  sure  and  definite  characteristic  of  defec- 
tive chromatic  sensation.  All  colors  do  not,  however,  meet 
this  equally  well :  hence  it  is  worth  while  to  establish  cer- 
tain rules  as  to  a  correct  choice. 

"  The  faculty  possessed  by  the  eye  of  distinguishing  colors, 
and  that  of  defining  the  degrees  of  light  and  color  (of 
"saturation")  are  relatively  very  different ;  but  these  spe- 
cial faculties  have  this  in  common,  that  they  have  their 
maximum  activity  in  a  certain  intermediary  region  of  abso- 
lute intensity  of  light,  and  their  minimum  at  the  two  limits 
of  this  region.  Just  as  we  experience  the  most  difficulty  in 
distinguishing  between  the  shades  of  intensity  of  light  by 
a  very  feeble  or  very  strong  illumination,  so  it  is  difficult  for 
us  to  distinguish  colors  slightly  or  strongly  luminous,  or  the 
deepest  and  the  lightest.  It  is  therefore  necessary  to  select 
as  a  suitable  color  for  discovering  a  feeble  chromatic  sense 
either  the  lightest  or  darkest  shades.  The  well-defined 
kinds  and  degrees  of  a  defective  chromatic  sense  confound 
only  colors  of  mean  intensity.  But  in  this  case,  also,  it  is  a 
question  what  tones  of  color  to  choose.  For  my  choice  I 
have  been  guided  by  the  Young-Helmholtz  theory,  and  for 
the  reason  that  I  have  proposed  my  method  in  support  and 
proof  of  that  theory.  As  a  fact  the  examination  of  thou- 
sands of  persons  has  convinced  me  of  the  excellence  of  my 
choice.  I  have  selected,  to  determine  whether  the  chromat- 
ic sense  is  or  is  not  defective,  a  light  green  (dark  green  may 
be  also  used),  because  green,  according  to  the  theory,  is  the 
whitest  of  the  colors  of  the  spectrum,  and  consequently  is 
most  easily  confused  with  gray.     For  the  diagnosis  of  the 


210  COLOR-BLINDNESS  : 

especial  kinds  of  partial  color-blindness,  I  have  selected 
purple  (pink)  ;  that  is,  the  whole  group  of  colors  in  which 
red  (orange)  and  violet  (blue)  are  combined  in  nearly  equal 
proportions,  at  least  in  such  proportions  that  no  one  suffi- 
ciently preponderates  over  the  others,  to  the  normal  sense, 
so  as  to  give  its  name  to  the  combination.  This  is  the 
reason  for  this  choice.  Purple  occupies  a  singular  position 
amongst  colors :  although  a  mixed,  it  is,  we  know  a  color 
as  well  "saturated"  as  the  colors  of  the  spectrum,  and 
might  be,  from  this  point  of  view,  classed  with  them, 
although  it  is  not  found  in  the  spectrum.  In  fact,  it  has 
been  regarded  as  the  eighth  color  of  the  spectrum,  closing 
the  circle  of  saturated  colors.  Purple  is  of  especial  impor- 
tance in  the  examination  of  the  color-blind,  for  the  reason 
that  it  forms  a  combination  of  two  fundamental  colors  — 
the  two  extreme  colors  —  which  are  never  confounded  with 
each  other.  In  fact,  from  a  color-blind  point  of  view,  one 
of  two  things  must  happen,  according  to  the  theory :  either 
it  excites  but  one  kind  of  perceptive  organs,  or  it  excites 
them  all.  It  appears,  then,  either  like  a  simple  color,  —  that 
is  to  say,  like  one  of  the  two  colors  of  the  combination,  —  or 
like  white  (gray.)  Experiment  has  confirmed  this  hypothe- 
sis. Our  sample  colors,  therefore,  are  the  two  complemen- 
tary colors  of  each  other,  —  green  and  purple. 

"In  the  examination  of  the  chromatic  sense  of  a  large 
number  of  individuals,  it  is,  of  course,  of  importance  to  de- 
cide quickly,  first,  whether  the  chromatic  sense  of  the  indi- 
vidual is  or  is  not  normal.  It  is  only  after  establishing  the 
existence  of  a  defect  that  its  nature  or  degree  must  be  de- 
termined. The  sample-colors  are  therefore  employed  with 
more  advantage  in  a  certain  order,  as  the  test  must  be  ac- 
complished as  a  whole,  according  to  a  plan  that  experience 
has  proved  the  surest,  most  rapid,  and,  finally,  most  suitable 
for  the  purpose. 

' '  MeOiod  of  Examination  and  Diagnosis. 
"  The  Berlin  worsteds  are  placed  in  a  pile  on  a  large  plane 
Burface,  and  in  broad  daylight ;  a  skein  of  the  test-color  is 
taken  from  the  pile,  and  laid  aside  far  enough  from  the 
others  not  to  be  confounded  with  them  during  the  trial ;  and 
the  person  examined  requested  to  select  the  other  skeins 


ITS   DANGEES   AND   ITS    DETECTION.  211 

most  resembling  this  in  color,  and  place  them  bj-  the  side  of 
the  sample.  In  the  first  place  it  is  necessary  that  he  should 
thoroughly  understand  what  is  required  of  him ;  that  is, 
that  he  should  search  the  pile  for  the  skeins  making  an  im- 
pression on  his  chromatic  sense  independent  of  any  name  he 
may  give  the  color,  similar  to  that  made  by  the  sample. 
The  examiner  should  explain  that  resemblance  in  every  re- 
spect is  not  necessary  ;  that  there  are  no  two  specimens 
exactly  alike ;  that  the  only  question  is  the  resemblance  of 
the  color ;  and  that,  consequently,  he  must  endeavor  to  find 
something  similar  of  the  same  shade,  something  lighter  and 
darker  of  the  same  color,  &c.  If  the  person  examined  can- 
not succeed  in  understanding  this  by  a  verbal  explanation,  we 
must  resort  to  action.  We  must  ourselves  make  the  trial  by 
searching  with  our  own  hands  for  the  skeins,  thereby  show- 
ing in  a  practical  manner  what  is  meant  by  a  shade,  and  then 
restoring  the  whole  to  the  pile,  except  the  sample-skein.  As 
it  would  require  much  time  to  examine  each  individual  in 
this  way,  it  is  advisable,  when  examining  a  large  number  at 
the  same  time,  to  instruct  all  at  once,  and,  moreover,  to  ask 
them  to  attentively  observe  the  examination  of  those  preced- 
ing them,  so  as  to  become  more  familiar  themselves  with 
the  process.  By  this,  time  is  saved,  without  loss  of  security ; 
for  no  one  with  a  defective  chromatic  sense  finds  the  correct 
skeins  in  the  pile  the  more  easily  from  the  fact  of  having  a 
moment  before  seen  others  looking  for  and  arranging  them. 
He  makes  the  same  characteristic  mistakes  ;  but  the  normal 
observer,  on  the  other  hand,  generally  accomplishes  his  task 
much  better  and  more  quickly  after  having  seen  how  it  must 
be  done,  and  this  is  the  advantage  of  our  method. 

"  The  colored  plate  is  for  the  purpose  of  assisting  the  ex- 
aminer in  the  choice  of  his  colors,  and  helping  him  decide 
the  character  of  the  trouble  from  the  mistakes  the  color- 
blind make.  We  have  attempted  to  represent  the  colors  we 
are  now  to  speak  of.     They  are  of  two  classes,  — 

"  1st,  The  colors  for  samples  (test-colors)  ;  that  is,  those 
which  the  surgeon  presents  to  the  persons  examined  ;  and 

"  2d,  The  '  colors  of  confusion ; '  that  is  to  say,  those  which 
the  color-blind  selects  from  the  heap  of  worsteds,  because  he 
confuses  them  with  that  of  the  sample. 

"  The  first  are  horizontal  on  the  plate,  and  marked  with 


212  COLOR-BLINDNESS  : 

Roman  numerals  ;  the  second  are  vertical,  under  the  test- 
colors,  and  marked  with  Arabic  figures. 

"  We  have  already  described  why  such  a  table  cannot  be 
constructed  with  a  small  number  of  colors  adaj^ted  to  all 
color-blind.  It  is,  moreover,  often  difficult  —  even  impossi- 
ble—  to  accurately  give  the  brilliant  colors  the  worsteds 
have.  The  test-colors,  with  the  exception  of  II.,  answer  the 
purpose ;  but  the  others  not  so  well,  from  the  difficulty  we 
have  spoken  of,  and  because  all  color-blind  do  not  choose 
the  same  shades  of  the  same  color. 

"  The  colored  table  is  not  intended  to  be  directly  used  to 
test  with,  though  it  may  serve  this  purpose  occasionally.  It 
is  rather  to  simply  assist  the  surgeon  in  his  choice  of  the 
correct  test-colors,  and  help  him  diagnosticate  the  special 
form  of  color-blindness. 

"  As  to  the  conformity  between  the  worsteds  the  color- 
blind take  from  the  heap  and  the  confusion-colors  of  the  plate, 
we  must  simply  rely  on  the  tone,  and  not  much  on  the  in- 
tensity of  light  or  degree  of  saturation.  In  all  cases  where 
we  have  to  vary  from  this  rule,  we  must  hold  to  the  relative 
rather  than  the  absolute  saturation.  The  confusion-colors 
of  our  table  are  only  to  illustrate  the  color-blind's  mistakes, 
and  this  purpose  they  serve  perfectly.  Having  made  this 
explanation,  we  will  pass  directly  to  the  test  itself.  The 
following  are  the  directions  for  conducting  this,  and  making 
our  diagnosis  from  the  results  :  — 

"  Test  I.  —  The  green  sample  is  presented.  This  sample 
should  be  the  palest  shade  (the  lightest)  of  very  pure  green, 
which  is  neither  a  yellow  green  nor  a  blue  green  to  the  nor- 
mal eye,  but  fairly  intermediate  between  the  two,  or  at  least 
not  verging  upon  yellowish  green. 

"  Rule.  —  The  examination  must  continue  until  the  one 
examined  has  placed  near  the  sample  all  the  other  skeins  of 
the  same  shade,  or  else,  with  these  or  separately,  one  or  sev- 
eral skeins  of  the  class  corresponding  to  the  '  colors  of  con- 
fusion '  (1-5),  until  he  has  sufficiently  proved  by  his  manner 
of  doing  it  that  he  can  easily  and  unerringly  distinguish  the 
confused  colors,  or  until  he  has  given  proof  of  unmistakable 
difficulty  in  accomplishing  this  task. 

'■'■Diagnosis.  —  He  who  places  beside  the  sample,  one  of 
the  '  colors  of  confusion  '  (1-5)  —  that  is  to  say,  finds  that  it 


ITS   DANGERS   AND    ITS   DETECTION".  213 

resembles  the  '  test-color ' —  is  color-blind.  He  who,  without 
being  quite  guilty  of  this  confusion,  evinces  a  manifest  dis- 
position to  do  so,  has  a  feeble  chromatic  sense. 

"  Remark.  —  We  must  remember  that  we  might  have 
taken  more  than  five  colors  for  '  confusion  ; '  but  we  have 
here  in  view,  not  every  kind  of  defective  color-sense,  but  only 
those  important  in  the  business  of  railways.  The  number 
of  colors  on  the  plate  is  therefore  sufficient,  as  these  are  the 
most  important  and  most  common. 

"  As  to  iS'o.  1,  which  represents  the  gray  color,  we  would 
remark  that  too  much  stress  must  not  be  laid  on  the 
light  intensity,  or  on  slight  differences  in  the  color-tone. 
This  is  especiall}^  true  of  the  gray  skeins  which  the  exam- 
ined puts  with  the  sample.  If  we  need  determine  only 
whether  a  person  was  color-blind  or  not,  no  further  test 
would  be  necessary.  If  we  want  to  know  the  kind  and 
degree  of  his  color-blindness,  then  we  must  go  on  with 
another  test. 

"  Test  II.  —  A  purple  skein  is  shown  the  examined. 
The  color  should  be  midway  between  the  lightest  and  dark- 
est. It  will  only  approach  that  given  in  II.  of  the  plate, 
because  the  color  of  the  worsted  is  much  more  brilliant  and 
saturated,  and  more  towards  the  blue. 

'■'-Rule. — The  trial  must  be  continued  until  the  one  ex- 
amined has  placed  near  the  sample  all  or  the  greater  part  of 
the  skeins  of  the  same  shade,  or  else,  simultaneously  or  sep- 
arately, one  or  several  skeins  of  '  confusion  '  (6-9).  He  who 
confuses  the  colons  selects  either  the  light  or  deep  shades  of 
blue  and  violet,  especially  the  deep  (6  and  7),  or  the  light 
or  deep  shades  of  one  kind  of  green  or  gray  inclining  to 
blue  (8  and  9). 

"  Diagnosis.  —  1.  He  who  is  color-blind  by  the  first  test, 
and  who,  upon  the  second  test,  selects  only  purple  skeins,  is 
incompletely  color-blind. 

"2.  He  who,  in  the  second  test,  selects  with  purple  only 
blue  and  violet,  or  one  of  them,  is  completely  red-blind. 

"  3.  He  who,  in  the  second  test,  selects  with  purple  only 
green  and  gray,  or  one  of  them,  is  completely  green-blind. 

"  Remark.  —  The  red-blind  never  selects  the  colors  taken 
by  the  green-blind,  and  vice  versa.  Often  the  green-blind 
places  a  violet  or  blue  skein  side  of  the  green,  but  only  the 


214  COLOR-BLINDNESS  : 

brightest  shades  of  these  colors.  This  does  not  influence 
our  diagnosis. 

"  The  fact  that  many  green-blind  select  in  this  test,  be- 
sides gray  and  green  or  one  of  these  colors,  also  bright  blue, 
has  led  to  misunderstanding.  Some  have  from  this  con- 
cluded that  red  and  green  blindness  may  exist  together  in 
the  same  individual ;  others  have  thought  that  these  two 
kinds  of  color-blindness  were  not  readily  distinguished  by 
ray  method.  The  former  conclusion  is  not  correct.  The 
two  kinds  have  great  similarity  in  close  unanimity  with  the 
theory,  but  differ  in  innumerable  slight  variations.  They 
are  nevertheless,  in  view  of  the  theory,  to  be  considered  as 
two  sharply  defined  species. 

"  The  second  conclusion  can  only  arise  from  not  under- 
standing and  not  using  the  method  correctly.  The  especial 
purpose  of  this  method  must  here  be  kept  constantly  in 
view,  and  that  is  to  find  a  characteristic  of  the  defective 
color-perception  of  the  examined.  This  characteristic,  or 
sign,  with  green-blindness,  is  the  confusing  the  purple  with 
gray  or  green,  or  both.  This  confusion  is  the  point  to  be 
determined :  all  else  may  be  neglected.  A  complete  color- 
blind, who  confuses  purple  with  gray  or  green  (bluish  green), 
or  both,  is  green-blind,  do  icliat  else  lie  may.  This  is  the  rule, 
and  it  will  not  fail  the  careful  and  observant  examiner  who 
understands  the  application  of  the  test.  On  the  contrary,  it 
is  often  possible,  in  marked  cases  of  incomplete  color-blind- 
ness, to  decide  which  kind  we  have  by  the  way  the  examined 
acts  with  his  hands. 

"  We  do  not  mean  by  this  that  the  diagnosis  is  always 
very  easy.  Practice  and  knowledge  are  necessary.  More- 
over, as  we  have  often  said,  there  is  a  long  series  of  degrees 
from  incomplete  color-blindness  to  normal  vision  on  the  one 
side,  and,  on  the  other,  to  complete  color-blindness.  There 
must  naturally  be  a  border  line  where  differences  of  the  two 
kinds  of  color-blindness  cease  to  be  recognized. 

"  The  examination  may  end  with  this  test,  and  the  diag- 
nosis be  considered  as  perfectly  settled.  It  is  not  even  neces- 
sary, practically,  to  decide  whether  the  color-blindness  is 
red  or  green.  But  to  be  more  entirely  convinced  of  the 
relation  of  complete  color-blindness  wdth  the  signal-colors, 
and  especially  to  convince,  if  necessary,  the  railway  em- 


ITS   DANGERS   AND  ITS   DETECTION.  215 

ployes  and  others  who  are  not  specialists,  the  examination 
may  be  completed  by  one  more  trial.  The  one  we  are  going 
to  mention  is  not  necessary  to  the  diagnosis,  and  only  serves 
to  corroborate  the  investigation. 

"  Test  III.  —  The  red  skein  is  presented  to  the  subject. 
It  is  necessary  to  have  a  vivid  red  color,  like  the  red  flag 
used  as  signals  on  railways.  The  color  should  be  that  of 
II.  h  of  the  plate,  rather  towards  yellowish  red. 

"Rule.  —  This  test,  which  is  applied  only  to  those  com- 
jDletely  color-blind,  should  be  continued  until  the  person  ex- 
amined has  placed  beside  the  specimen  all  the  skeins  belong- 
ing to  this  shade  or  the  greater  part,  or  else,  separately,  one 
or  several  'colors  of  confusion'  (10-13).  The  red-blind 
then  chooses,  besides  the  red,  green  and  brown  shades,  which, 
(10-11),  to  the  normal  sense,  seem  darker  than  red.  On  the 
other  hand,  the  green-blind  selects  opposite  shades,  which 
apj)ear  lighter  than  red  (12-13). 

'■'■  Remark. — Every  case  of  complete  color-blindness  dis- 
covered does  not  always  make  the  precise  mistakes  we  have 
just  mentioned  in  the  preceding  examinations.  These  ex- 
ceptions are  either  instances  of  persons  ^dth  a  comparatively 
inferior  degree  of  complete  color-blindness,  or  of  color-blind 
persons  who  have  been  exercised  in  the  colors  of  signals, 
and  who  endeavor  not  to  be  discovered:  they  therefore 
usually  confound  at  least  green  and  brown;  but  even  this 
does  not  always  happen. 

"Additional  Note. — We  have  not  given  rules  for  dis- 
covering total  color-blindness,  because  we  have  not  found 
any  cases  of  this  kind.  If  any  such  should  be  found,  they 
will  be  recognized,  according  to  the  theory,  by  a  confusion 
of  every  shade  having  the  same  intensity  of  light. 

"  Violet-blindness  will  be  recognized  by  a  genuine  confu- 
sion of  purple,  red,  and  orange  in  the  second  test.  The 
diagnosis  should  be  made  with  discrimination.  The  first 
test  often  shows  blue  to  be  a  'color  of  confusion.'  This 
may,  in  certain  cases,  be  the  sign  of  violet-blindness,  but  not 
always.  We  have  not  thought  it  advisable  to  admit  defects 
of  this  kind  :  only  the  most  marl^ed  cases,  that  other  exam- 
inations establish  as  violet  color-blindness,  should  be  reck- 
oned in  the  statistics.  Finally,  to  acquire  a  desirable  uni- 
formity, it  is  necessary  to   add,  that,  in   the  preparatory 


216  COLOB-BLINDNESS  : 

examination,  it  is  my  habit  to  indicate  in  the  journal,  espe- 
cially kept  for  that  purpose,  cases  of  complete  color-hUndnes^s 
by  2  (2  R.,  2  G.,  2  V.),  those  of  incomplete  blindness  by  1, 
and  those  of  feeble  chromatic  sense  by  0.5  (0.5  R.,  0.5  G., 
0.5  V.)." 

Professor  Holmgren  lias  subsequently  published 
a  further  explanation  of  this  method  of  testing 
for  color-blindness,  which  is  not  in  the  Swedish, 
French,  or  German  edition  of  his  book,  nor  in  the 
abridged  translation  of  the  Smithsonian.  I  there- 
fore add  it  here  in  full,  as  it  is  very  important  for 
examiners :  — 

"  The  Detection  of  Color-Blindness  among  Large  Numbers. 

"  Those  who,  in  the  collection  of  material  for  scientific 
research  or  for  the  practical  purpose  of  control  among  rail- 
road employes  and  sailors,  have  to  test  the  color-sense  of 
large  numbers  of  persons,  in  order  to  separate  the  color-blind 
from  the  normal,  and  ascertain  the  former's  kind  of  defect, 
will  have  found  the  great  value  of  a  method  which  is  rapid 
and  sure  in  its  working.  This  is  very  satisfactorily  fulfilled 
by  my  method  with  the  worsteds  as  originally  given.  But, 
to  gain  still  further  time,  —  that  is,  to  increase  the  rapidity 
of  the  examination  without  detracting  from  its  surety  and 
practicability,  —  1  have  lately  somewhat  simplified  the 
method  of  working,  whilst  retaining  the  same  principle, 
thereby  gaining  a  third  or  more  of  the  necessary  time. 

"  As  my  method  has  been  so  favorably  received,  and  its 
use  spread  so  rapidly  and  so  widely,  I  think  it  right  to  give 
a  brief  explanation  of  this  modification  for  the  benefit  of 
professional  men. 

"  The  worsted  method,  from  the  many  colors  and  the 
movable  character  of  the  material,  is  very  readily  appli- 
cable to  any  special  case.  It  can,  as  no  other,  be  variously 
modified  to  meet  circumstances.  We  are  here  dealing  with 
practical  contrivances  of  more  general  value,  which,  simple 
as  they  may  seem,  were  only  learned  by  long  experience. 
They  partly  relate  to  the  worsteds,  and  partly  to  the  par- 
ticular way  of  carrying  out  the  test  itself. 


ITS   DANGERS  AND   ITS   DETECTION.  217 

*'  I.  The  right  choice  of  colors  for  the  collection  of  \\'orsteds 
to  be  used  helps  not  a  little  to  shorten  the  examination.  All 
who  are  practically  acquainted  with  my  method  have  had 
their  patience  tried  by  the  want  of  readiness  of  the  normal- 
eyed  in  picking  out  the  lighter  of  the  green  skeins  corre- 
sponding to  the  sample  from  the  other  green  shades  of  the 
bundle.  In  my  book  I  had  to  devote  many  pages  to  this 
point.  As  I  there  said,  it  is  the  normal-eyed  who  cause 
most  loss  of  time,  from  their  peculiar  misappreciation  of 
the  green  colors,  which  is  of  no  importance  for  the  main 
object,  and  generally  to  be  corrected.  The  color-blind,  on 
the  other  hand,  make  no  such  errors,  but  other  very  different 
and  characteristic  mistakes,  and  generally  very  quickly. 

"  There  is  therefore  considerable  gained  if  we  can  help 
the  normal-eyed,  and  still  not  change  the  conditions  of  the 
test  for  the  color-blind.  This  may  be  done  by  leaving  out 
of  the  bundle  of  w^orsteds  all  the  green  colors,  except  the 
lighter  ones  belonging  to  Test  I.  In  this  primary  test  the 
choice  for  the  normal-eyed  w^ill  be  within  quite  narrow  lim- 
its ;  and,  as  experience  has  shown,  they  are  quickly  through. 
The  color-blind,  however,  to  whom  the  other  colors,,  or  so- 
called  confusion-colors,  resemble  the  green,  has  as  great  a 
choice  as  before. 

"  The  removal  of  the  superfluous  greens  is  therefore  sim- 
plifying the  method,  and  an  improvement  from  the  saving 
of  time.  We  lose  also  nothing  from  the  certainty  of  the 
color-blind's  distinguishing  himself  from  the  normal-eyed. 
We  must,  however,  not  fail  to  remember,  that,  though  this 
renders  the  method  more  precise  as  to  the  practical  point, 
yet  it  also  limits  it.  Opportunity  for  observing  certain 
other  points  is  lost.  For  instance,  we  have  reduced  to  a 
minimum  the  chance  of  watching  the  evident  difference  in 
the  intelligence,  practice,  and  education  of  the  examined, 
all  which  possesses  a  certain  psychological  interest. 

"  When,  as  in  railroad  employes  and  sailors,  we  are  con- 
cerned alone  with  rapidly  detecting  the  commonest  forms 
and  degrees  of  color-blindness,  —  namely,  complete  red  and 
green  blindness  and  incomplete  color-blindness,  —  we  may 
of  course,  also,  leave  out  the  bright-blue  worsteds,  and,  with 
Test  II.,  the  bright-violet  colors.  But  in  Test  II.  we  must, 
for  the  green-blind,  leave  all  the  grades  of  the  bluish-green 


218  COLOE-BLINDNESS  : 

confusion-color,  No.  9  of  the  plate.  I  will  here  speak  only 
of  the  green  colors,  because  they  are  of  most  importance, 
and  sufficiently  indicate  the  principle  of  the  simplification. 

"II.  As  to  the  carrying-out  of  the  test,  it.  could  not  be 
quicker  than  the  selecting  at  once  from  hundreds  of  persons 
the  color-blind  from  the  normal-eyed.  Such  an  examina- 
tion of  a  mass  of  people  is  conceivable,  but  not  practical, 
because  the  necessary  surety  and  certainty,  as  well  as  the 
classification  of  the  color-blind,  demand  a  separate  exami- 
nation of  each  individual. 

"  This  simplification,  however,  allows  of  a  larger  number 
of  persons  together  being  prepared  for  the  test.  A  principle 
of  the  method  is  the  fact  that  the  examined  does  not  have 
to  answer  any  question,  but  is  simply  compelled  to  show 
the  character  of  his  color-sense  by  a  definite  action.  This 
of  course  implies  his  being  instructed  as  to  precisely  what 
he  is  to  do.  Just  how  this  is  done,  and  the  test  conducted, 
has  no  small  effect  on  the  rapidity  of  the  whole  examina- 
tion. If  each  person  is  thoroughly  instructed  as  to  what  he 
is  to  do,  he  finds  it  extremely  simple,  and  rapidly  makes 
the  test,  whether  he  is  color-blind  or  not. 

"  The  certainty  of  the  test  is  not  interfered  with  whilst 
its  rapidity  is  increased  by  giving  the  preparatory  instruc- 
tion to  a  large  number  together.  It  adds  to  rapidity,  if  all 
the  examined,  or  as  many  as  possible,  see  each  individual 
tested.  We  need  not  fear  that  the  color-blind  can  learn 
any  thing  by  seeing  what  the  normal-eyed  do.  The  effect 
of  the  examination  is  all  the  more  striking  and  convincing 
when  a  number  have  regularly  gone  through  with  the  test 
correctly,  and  then  one  comes  who  has  for  some  time  stood 
among  the  lookers-on,  and  makes  the  characteristic  mis- 
takes of  the  color-blind.  This  is  always  the  case.  On  the 
other  hand,  a  normal-eyed  may  thus  learn  to  imitate  the  mis- 
takes of  a  color-blind.  In  testing  numbers  thus,  it  Vv^ould, 
however,  but  rarely  happen  that  any  one  was  interested  in 
simulating  color-blindness.  Even  in  this  case  counterfeit- 
ing the  color-blind  is  readily  detected  by  the  subsequent 
control  examination,  and  hence  quite  harmless. 

"  With  these  j)reliminary  remarks,  the  practical  rules  for 
quickly  testing  large  numbers  for  the  common  forms  of 
color-blindness  may  be  briefly  given  as  follows  :  — 


ITS   DAKGERS   AND  ITS   DETECTIOX.         219 

"1st,  In  the  first  test,  we  leave  out  of  the  bundle  of  wor- 
steds all  the  greens,  with  the  single  exception  of  those  to 
which  the  test-color  I.  belongs  (vide  the  plate),  and  which 
should  consist  of  about  five  grades  or  shades. 

"  2d,  AVhen  using  the  second  test,  we  put  in  the  bundle  or 
near  it  the  bluish  greens  of  \'Trrious  intensities,  correspond- 
ing to  the  confusion-color  Xo.  9. 

"3d,  Before  commencing,  let  some  fifty  stand  round  the 
table  on  wliich  the  worsteds  are  placed,  or  be  so  arranged 
that  they  can  see  what  takes  place  on  the  table.  Then  call 
attention  to  the  test  as  follows  :  — 

"  4th,  We  hold  up  the  five  green  worsteds  before  the  ex- 
amined, and  tell  them  to  carefully  observe  them,  so  as  to 
readily  and  quickly  pick  them  out  from  all  the  mixed-up 
colors.  Then  we  place  test  L,  the  brightest  of  the  five,  to 
one  side,  and  mix  the  others  well  in  the  bundle.  With  our 
own  hand  we  rapidly  pick  these  out  again,  and  lay  them 
with  the  first  to  one  side  :  in  other  words,  we  perform  the 
test  just  as  it  should  be,  and  this  we  can  repeat  as  often  as 
is  useful  in  hastening  the  examination. 

"  5th,  After  this  preparation,  we  let  the  examined  come 
one  after  the  other  to  the  table,  and  repeat  the  test  they 
have  seen  done.  The  others  must  keep  quiet,  and  neither 
by  laughing,  calling  out,  or  signs,  interfere  with  the  one 
being  tested. 

"  6th,  When  any  has  shown  himself  color-blind  by  this 
test,  then,  for  the  differential  diagnosis.  Test  11.  will  be  used. 
Test  III.  need  not  be  at  all. 

"  7th,  As  in  general  the  test  is  rapidly  made,  a  feeble  sense 
of  color  is  shown  by  great  slowness  in  the  manifestation. 

"We  may  thus  with  perfect  certainty  test  a  hundred  or 
more  individuals  in  an  hour,  especially  soldiers  or  those 
under  discipline. 

"  Finally,  1  would  remark,  that,  with  this  method  of  test- 
ing, we  need  not  speak  a  word,  of  which  experience  has 
convinced  me.  We  may  test  the  dumb  without  even  know- 
ing their  sign-language-.  This  method,  therefore,  recom- 
mends itself  above  all  others  for  testing  imcivilized  people 
whose  language  is  unknown  to  the  examiner.  Such  exam- 
inations, which  I  have  already  carried  out  to  a  small  extent, 
will  be  of  interest  in  reference  to  the  question  of  develop- 
ment of  the  color-sense  in  general." 


220  COLOR-BLINDNESS  : 

I  have  thus  given  Holmgren's  precise  descrip- 
tion of  the  worsted-test  as  he  carries  it  out.  My 
own  experience  has  been  to  lead  me  to  employ  the 
seemingly  longer  method  with  the  larger  number 
of  greens.  Therefore  I  add  here  the  exact  de- 
scription given  in  the  original  in  full  of  the  way 
of  conducting  it.  To  ^hose  of  my  readers  who 
may  consider  it  superfluous  or  unnecessarily  ex- 
tended, I  would  say,  try  and  go  on  with  the  test 
alone  amongst  those  with  whom  a  mistake  on 
your  part  would  be  fatal,  and  you  will  gladly  turn 
back  and  carefully  study  this  following  chapter, 
with  thanks  to  Holmgren  for  it. 


ITS   DA^'GEES   AND   ITS   DETECTION.         221 


CHAPTER  XX. 

SPECIAL  DIEECTIOXS  FOR  COXDUCTIXG  THE  TEST. 

"  The  method,  as  we  have  said,  plays  an  important  part 
in  an  examination  of  this  kind,  not  only  from  the  principles 
upon  which  it  rests,  but  also  from  the  manner  in  which  it 
is  used.  The  best  plan  for  directing  how  to  proceed  is 
by  oral  instructions  and  de  visu  ;  but  here  we  are  obliged  to 
accomplish  this  by  description.  IN'ow,  this  is  always  defec- 
tive in  some  respects,  especially  if  we  wish  to  be  brief. 
What  has  been  said  would  evidently  sufl&ce  for  an  intelli- 
gent and  experienced  physician ;  but  it  may  not  be  superflu- 
ous to  enter  still  further  into  detail  to  provide  against  any 
possible  difficulties  and  loss  of  time.  The  object  of  the 
examination  is  to  discover  the  nature  of  a  person's  Chro- 
matic sense.  Xow,  as  the  fate  of  the  one  to  be  examined 
and  that  of  others  depend  upon  the  correctness  of  the  judg- 
ment pronounced  by  the  examiner,  and  that  this  judgment 
should  be  based  upon  the  manner  in  which  the  one  exam- 
ined stands  the  trial,  it  is  of  importance  that  this  trial 
should  be  truly  what  it  ought  to  be,  —  a  trial  of  the  nature  of 
the  chromatic  sense,  and  nothing  else,  —  an  end  that  will  be 
gained  if  our  directions  are  strictly  followed.  It  is  not  only 
necessary  that  the  examiner  carefully  observe  them,  —  which 
does  not  seem  to  us  difficult,  —  but  that  he  also  take  care 
that  the  individual  examined  does  thoroughly  what  is  re- 
quired of  him.  This  is  not  always  as  easy  as  one  might 
suppose.  If  it  were  only  required  to  examine  intelligent 
people,  familiar  with  practical  occupations  and  especially 


222  COLOE-BLINDNESS  : 

with  colors,  and  with  no  other  interest  connected  with  the 
issue  of  the  examination  than  to  know  whether  they  are 
color-blind  or  not,  the  examination  would  be  imiform  and 
mechanical ;  but  it  is^  required  to  examine  people  of  va- 
rious degrees  of  culture,  all  of  whom,  besides,  have  a  per- 
sonal interest  in  the  issue  of  the  examination.  Different 
peojile  act  very  differently  during  the  examination  for  many 
reasons.  Some  submit  to  it  without  the  least  suspicion  of 
their  defect ;  others  are  convinced  that  they  possess  a  nor- 
mal sense.  A  few  only  have  a  consciousness,  or  at  least 
some  suspicion,  of  their  defect.  These  last  can  often  be 
recognized  before  the  least  examination  by  keeping  behind 
the  others,  by  attentively  following  the  progress  of  the  trial, 
but,  if  allowed,  willingly  remaining  to  the  last.  Some  are 
quick ;  others,  slow.  The  former  approach  unconcernedly 
and  boldly ;  the  latter,  with  over-anxiety  and  a  certain 
dread.  Some  have  been  perhaps  already  tested,  and  prac- 
tised themselves  in  preparation  for  the  trial ;  others  have 
never  been  familiar  with  colors.  Among  those  already 
tested  may  be  some  color-blind.  Some  of  these  latter  are 
uncertain  about  their  mistakes,  and  act  with  great  care ; 
whilst  others  again  are  practised  in  distinguishing  the  sig- 
nals and  hence  conclude  that  their  color-sense  is  perfect. 
They  make  the  trial  quickly,  and  without  thought ;  of  course 
regularly  making  the  mistakes  characteristic  of  their  spe- 
cial form  of  color-blindness. 

"The  majority,  however,  desire  to  perform  their  task  as 
well  as  possible;  that  is,  to  do  what  the  normal-eyed  does. 
This  of  course  assists  in  testing  them,  provided  it  does  not 
lead  to  too  great  care,  as  then  the  testing  the  color-blind  is 
more  difficult;  the  trouble  being  that  much  time  is  thus 
wasted.  Only  a  very  small  part  have  a  contrary  desire ; 
namely,  to  pass  for  color-blind,  though  normal-eyed.  We 
will  speak  of  these  later,  and  now  only  concern  ourselves 
with  those  who  stand  the  test  in  good  faith  with  the  desire 
to  appear  normal,  though  perhaps  color-blind. 

"  The  trial  generally  goes  on  rapidly  and  regularly.  We 
will  only  mention  those  hinderances  and  peculiarities  w^hich 
most  frequently  occur.  The  examiner  must  watch  that  no 
mititake  is  made  from  not  understanding.  The  names  of 
the  colors  need  never  be  used,  except  to  ascertain  if  the 


ITS   DAXGEES   AND  ITS   DETECTION.  223 

name  learned  hides  the  subjective  color-sensation,  or  to  find 
the  relation  between  the  name  the  color-blind  employs  and 
his  color-perception. 

"  The  person  examined  who  thinks  more  of  names  than 
the  test  itself  (this  being  generally  a  sign  of  school-learn- 
ing) selects  not  only  the  worsteds  of  the  same  shades, — that 
is,  those  of  the  same  color  to  his  eye,  —  but  all  which  gener- 
ally have  the  name  of  this  color ;  for  instance,  in  the  first 
test  I.,  not  only  the  green  like  the  sample,  but  all  that  are 
green ;  and  with  the  second  test,  not  only  the  purple  (and 
what  are  generally  called  red),  but  all  which  looh  reddish, 
scarlet,  cinnabar,  or  sealing-wax  red.  This  is  of  no  impor- 
tance ;  for  those  who  only  do  this  have  scarcely  such  defec- 
tive chromatic  sense  as  we  are  concerned  with.  He  is  either 
normal-eyed  or  violet-blind.  Simply  as  a  test  of  violet- 
blindness  in  the  interest  of  science,  we  can  go  on  with  the 
trial,  and  ascertain  how  far  the  grouping  of  the  two  colors 
was  due  to  a  confusion  of  names  or  to  defective  color-percep- 
tion. Otherwise  this  examination  does  not  concern  the  prac- 
tical point  we  aim  at. 

"  Under  any  circumstance  it  is  better  to  correct  the  mis- 
takes just  mentioned,  when  arising  from  misunderstanding, 
and  even  necessary,  in  reference  to  mistakes  we  explained 
with  the  first  test.  It  might  be  said  that  it  was  sufficient 
if  the  examined  confounded  the  sample-color  with  green 
only  ;  that  it  was  indifferent  whether  he  distinguishes  care- 
fully between  the  various  kinds  of  green.  But,  in  fact,  this 
is  not  so  unimportant.  We  must  give  full  value  to  the 
determining  whether  the  infraction  of  the  rules  arises  from 
misunderstanding,  or  lack  of  practice  with  colors,  or,  finally, 
from  a  true  chromatic  defect.  To  include  all  that  is  green 
would  render  the  test  tedious  and  unpractical.  In  fact,  no 
little  judgment  has  been  exercised  in  the  selection  of  the 
very  lightest  shade  of  the  green  proposed  as  a  sample-color ; 
for  it  is  exactly  what  the  color-blind  most  readily  confounds 
with  the  colors  (1-5)  of  the  plate.  If  the  subject  were 
allowed  to  depart  from  the  narrow  limits  established  by  the 
trial,  it  would  include  every  shade  of  green ;  the  result  of 
u  hich  would  be  that  he  would  prefer  to  select  all  the  vivid 
shades,  and  thus  avoid  the  dangerous  ground  where  his 
defect  would  certainly  be  discoveted.     This  is  why   it  is 


224  COLOE-BLINDNESS  : 

necessary  to  oblige  him  to  keep  within  certain  limits,  con- 
fining him  to  pure  green  specimens,  and,  for  greater  security. 
to  recommend  him  to  select  especially  the  lightest  shades ; 
for,  if  he  keeps  to  the  darker  shades,  as  many  try  to,  he 
readily  passes  to  other  tones,  and  loses  himself  on  foreign 
ground,  to  the  great  loss  of  time  and  certainty  of  the  test. 
What  we  have  just  said  of  green  applies  also,  of  course,  to 
purple. 

"  The  principle  of  our  method  is  to  force  the  one  exam- 
ined to  reveal  himself,  by  an  act  of  his  own,  the  nature  of 
his  chromatic  sense.  Now,  as  this  act  must  be  kept  within 
certain  limits,  it  is  evident  that  the  examiner  must  direct 
him  to  a  certain  degree.  This  may  present,  in  certain  cases, 
some  difficulty,  as  he  will  not  always  be  guided,  and  does 
either  too  much  or  too  little.  In  both  cases  the  examiner 
should  use  his  influence,  in  order  to  save  time  and  gain 
certainty ;  and  this  is  usually  very  easily  done.  This  inter- 
vention is  of  course  intended  to  put  the  examiner  in  the 
true  path,  and  is  accomplished  in  many  ways,  according  to 
the  case  in  point. 

"  We  will  here  mention  some  of  the  expedients  we  have 
found  useful :  — 

"  (A)  Interfering  lulien  the  Examined  select  too  many  Colors. 

"  It  is  not  always  easy  to  confine  the  one  examined  with- 
in the  limits  of  the  method.  He  easily  slips  in  the  first 
test,  for  example,  a  yellow-green  or  blue-green  skein  among 
the  others,  and,  as  soon  as  there  is  one,  others  follow  usually ; 
and  it  thus  happens  that  in  a  few  moments  he  has  a  whole 
handful  of  yellow-green,  a  second  of  blue-green,  a  third  of 
both  these  shades  at  the  same  time.  Our  process  has 
assisted  us  in  more  than  one  case  of  this  kind. 

"  (a)  When  the  person  examined  has  begun  to  select 
shades  of  one  or  several  other  colors  than  those  of  the 
sample,  his  ardor  is  arrested  by  taking  from  him  the  hand- 
ful of  skeins  he  has  collected,  and  asking  him  whether  his 
eye  does  not  tell  him  there  are  one  or  several  which  do  not 
match  the  others,  in  which  case  he  is  solicited  to  restore 
them  to  the  pile.  He  then  generally  remarks  that  there  is 
some  obscuration,  and  proceeds  in  one  of  the  following 
manners  :  — 


ITS   DANGERS    AXD   ITS   DETECTION.  225 

"1.  He  rejects,  one  after  the  other,  the  foreign  shades; 
so  that  the  correct  remain,  which  is  often  only  the  sample- 
skein.  He  is  shown  what  mistake  he  has  made.  Names 
are  used  to  remind  him  that  one  class  of  green  may  be 
yellow  green ;  and  another,  blue  green  :  and,  to  induce  him 
to  avoid  them,  he  is  advised  only  to  select  skeins  of  the 
same  shade  as  the  specimen,  although  they  be  lighter  or 
darker,  and  have  neither  more  yellow  nor  blue  than  that. 
If  his  first  error  arose  only  from  a  misconception  or  want 
of  practice  in  handling  colors,  he  begins  generally  to  under- 
stand what  he  has  to  do,  and  to  do  properly  what  is  required 
of  him. 

"2.  Or  else  he  selects  and  rejects  immediately  the  skein 
of  the  sample  itself.  This  proves  that  he  sees  the  difference 
of  color.  He  is  then  shown  the  skein  as  the  only  correct 
one,  and  asked  to  repeat  the  trial  in  a  more  correct  manner. 
He  is  again  put  on  the  right  track  as  just  before ;  and  the 
trial  proceeds  rightly,  unless  the  error  arose  from  a  defect  in 
the  chromatic  sense.  Many  seem,  however,  to  experience  a 
natural  difficulty  in  distinguishing  between  yellow  green 
and  blue  green,  or  the  dull  shades  of  green  and  blue.  This 
difficulty  is,  however,  more  apparent  than  real,  and  is  cor- 
rected usually  by  direct  comparison.  If  the  method  requir- 
ing the  name  of  the  color  to  be  given  is  used,  a  number  of 
mistakes  may  be  the  result.  If  a  skein  of  light  green  and 
light  blue  alone  are  presented  to  him,  asking  him  to  name 
them,  he  will  often  call  blu3  green,  and  green  blue.  But 
if,  in  the  first  case,  a  blue  skein  is  immediately  shown  him, 
he  corrects  his  mistake  by  saying  this  is  blue,  and  that 
green.  In  the  last  case  it  happens  so  mutatis  mutandis. 
This  is  not  the  place  for  an  explanation.  It  must  suffice  to 
say  that  the  error  is  corrected  by  a  direct  comparison  be- 
tween the  two  colors. 

"There  is,  according  to  the  theory,  one  class  of  the  color- 
bi'nd  —  violet-blind  —  who,  in  consequence  of  the  nature 
of  their  chromatic  sense,  and,  therefore,  notwithstanding 
the  comparison,  cannot  distinguish  blue  and  green.  But 
our  method  has  nothing  to  do  with  this  class  of  the  color- 
blind, because  such  are  not  dangerous  on  railways. 

'•(/^)  Another  Process.  — If  the  one  examined  place  by  the 
side  of  the  sample  a  shade,  for  instance,  of  yellow  green,  the 


226  COLOR-BLINDNESS  : 

examiner  places  near  this  another  shade,  in  which  there  is 
more  yellow,  or  even  a  pm-e  yellow,  remarking,  at  the  same 
time,  that,  if  the  first  suit,  the  last  must  also.  The  other 
usually  dissents  from  this.  He  is  then  shown,  by  selecting 
and  classing  the  intermediate  shades,  that  there  is  a  grada- 
tion, which  will  diverge  widely  if  logically  carried  out  as  he 
has  begun.  The  same  course  is  followed  vvith  colors  of  the 
blue  shades,  if  the  blue-green  were  first  selected.  He  sees 
the  successive  gradations,  and  goes  through  with  this  test 
perfectly  if  his  chromatic  sense  is  correct. 

"  To  ascertain  further  whether  he  notices  these  additions, 
or  the  tints  of  yellow  and  blue  in  the  green,  we  can  take 
ourselves  the  yellow  green  and  blue  green  to  ask  him  if  he 
finds  this  to  be  so.  We  can  judge  by  his  answer  of  his 
sense  with  regard  to  these  shades,  and  the  object  of  this 
investigation  is  accomplished. 

"  It  results  from  all  this  that  many  who  are  finally  con- 
sidered to  have  a  normal  chromatic  sense  may  occasionally 
cause  embarrassments.  In  the  main,  the  normal  observer 
of  this  kind  causes  greater  loss  of  time  than  the  color-blind. 
It  is  astonishing  to  see  with  what  rapidity  the  color-blind 
betray  their  defect.  At  least  it  is  found,  in  the  majority  of 
the  cases  examined  by  us,  that  the  first  skein  of  wool  selected 
from  the  pile  by  the  color-blind  in  the  first  test  was  one  of 
the  '  colors  of  confusion.' 

"  (B)  Interferhif)  when  the  Examined  select  too  few  Worsteds. 
"  Those  who  evince  too  great  slowness  also  require  the 
interferences  of  the  examiner  in  another  manner.  We  can 
lay  aside  here  those  cases  in  which,  at  the  sight  of  the  com- 
plex colors  of  the  heap  of  wool,  the  examined  finds  it  diffi- 
cult to  select  a  skein  resembling  the  sample  in  a  collection 
where  all  the  particular  colors  seem  to  differ  from  each  other, 
and  in  consequence  declares  immediately  that  he  can  find 
none  resembling  the  specimen.  It  is  replied  that  an  absolute 
resemblance  is  not  demanded,  and  that  no  one  asks  impossi- 
bilities ;  that  time  is  limited,  many  are  waiting,  &c.  But 
there  are  people  who  —  from  natural  slowness,  from  being 
unaccustomed  to  such  business,  from  fear  of  making  mis- 
takes, and  especially  if  previously  examined  and  suspected  of 
color-blindness,  or  from  many  other  motives  —  proceed  with 


ITS   DANGERS    AND   ITS   DETECTION.  227 

the  greatest  caution.  They  do  not  even  wish  to  touch  the 
AYOol ;  or  they  search,  select,  and  replace  with  the  greatest 
care  all  the  possible  skeins  without  finding  one  correspond- 
ing with  the  sample,  or  that  they  wish  to  place  beside  it. 
Here  then  are  two  cases  :  on  one  hand,  too  much  action  with 
the  fingers,  without  result;  on  the  other,  too  little  effort. 
The  examiner  is  forced  to  interfere  in  both  cases. 

"  (a)  At  the  time  of  a  too  great  manual  action,  without 
corresponding  practical  result,  the  examiner  must  be  care- 
ful that  the  eye  and  hand  act  simultaneously  for  the  accom- 
plishment of  the  desired  end. 

"  Some  people  forget  that  the  hands  should  be  subservi- 
ent to  the  eye  in  this  trial,  and  not  act  independently.  Thus 
they  are  often  seen  to  fix  their  eyes  on  one  side  while  their 
hands  are  engaged  on  the  other.  This  should  be  corrected, 
so  as  to  save  time  and  avoid  further  labor.  AVhen,  from  the 
manual  activity  of  the  one  examined,  or  by  the  unobserved 
aid  of  the  examiner,  all  the  correct  skeins,  or  only  a  portion, 
are  found  in  the  pile,  it  is  wise  to  stop,  and  invite  the  former 
to  cross  his  hands  behind  his  back,  to  step  back  a  pace,  and 
quietly  consider  all  the  skeins,  and,  as  soon  as  his  eye  has 
met  one  of  those  for  which  he  is  looking,  to  extend  his  hand 
and  take  it.  The  best  plan  is  to  advise  him  to  look  first  at 
the  sample,  and  then  at  the  pile,  and  to  repeat  this  manoeu- 
vre until  his  eyes  find  wdiat  he  is  looking  for. 

"  This  stratagem  generally  succeeds  when  nervousness 
from  over-anxiety  causes  his  hands  to  tremble  ;  but  it  is 
not  always  easy  to  induce  him  to  keep  his  hands  behind  his 
back  until  the  moment  for  taking  the  skein  in  question. 

"  (J))  In  cases  of  great  caution,  the  trial  is  hastened,  if  the 
examiner  come  to  the  assistance  of  the  other  by  holding 
above  the  pile  one  skein  after  the  other,  and  requesting  him 
to  say  whether  it  resembles  the  color  of  the  sample  or  not. 
It  will  be  advisable  first  to  select  the  skeins  that  a  color- 
blind person  would  approve.  If  he  is  so,  he  will  approve  of 
the  selection,  and  the  question  is  settled  ;  if  not,  he  rejects 
them,  not  without  a  characteristic  smile,  or  with  an  expres- 
sion of  wounded  dignity.  This  also  enlightens  us  as  to  his 
chromatic  sense.  But  even  the  color-blind  may,  in  such  a 
case,  refuse  what  is  presented,  especially  if  his  caution  is 
premeditated,  and  he  suspects  that  a  snare  is  intended.     It 


228  COLOR-BLINDNESS  : 

is  found  quite  frequently  that  he  rejects  the  correct  shades 
likewise  presented  with  the  others.  This  is  not  the  case 
when  one,  having  a  normal  chromatic  sense,  is  slow  and 
deliberative  when  subjected  to  the  test  under  this  form.  He 
has  an  eye  alive  to  the  correct  colors. 

"  One  process,  in  cases  of  this  last  kind,  is  to  select  false 
samples,  which  are  placed  quite  near  the  correct  one,  by  the 
side,  above,  or  below,  to  attract  the  attention  of  the  exam- 
ined from  the  right  side.  It  is  necessary  so  to  proceed  that 
the  true  sample  be  displaced  when  the  others  are  drawn  out, 
so  that  the  person  examined  may  see  it  move.  It  does  not, 
however,  always  happen  to  catch  his  eye.  The  best  means 
is  then  to  make  him  examine  the  wdiole,  with  his  hands 
behind  his  back,  and  invite  him  to  freely  make  his  choice. 
But,  whatever  the  process,  it  is  necessary,  in  every  case 
where  one  has  been  assisted  in  selecting  a  certain  number 
of  skeins  which  he  has  found  analogous  to  the  sample-color, 
to  make  a  rule  not  to  conclude  the  trial  without  examining 
into  the  effect  of  the  aid  accorded.  It  is  necessary  to  hold 
in  the  hand  the  approved  package,  and  ask  if  he  is  satisfied, 
or  if  he  would  desire  any  change.  If  he  approve  the  choice, 
the  diagnosis  is  established.  The  same  course  must  be  pur- 
sued with  the  defective  chromatic  sense,  that  the  trial  may 
be  made  wdth  or  without  assistance.  To  be  thorough,  the 
name  given  by  the  color-blind  to  the  colors  in  question  may 
be  likewise  asked. 

"  In  cases  where  any  one  suspected  of  color-blindness  has 
remained  some  time  to  see  the  trial  of  others,  and  where,  as 
often  happens,  he  has  remarked  the  samples  belonging  to  a 
required  green  shade,  he  may  of  course  profit  by  it  in  his 
own  trial.  But  this  can  be  prevented  by  furtively  conceal- 
ing one  or  two  of  these  samples.  If  he  seem  to  be  disposed 
to  confound  green  and  gray,  it  will  be  very  easy  to  entrap 
him.  If  w^e  do  not  succeed,  even  when  assisting  him,  in 
entrapping  him  in  this  snare,  the  hidden  samples  may  be 
put  back  into  their  places,  to  be  convinced  that  the  trial  is 
correct, 

"From  the  above,  it  is  seen  that  many  artifices  may  be 
necessary  in  our  examination.  It  may  be  regarded  as  an 
advantage  of  our  method  that  it  has  at  command  a  great 
variety  of  resources.     We  have  by  no  means  mentioned  all; 


ITS   DANGERS   AXD   ITS   DETECTION.  229 

and  yet  many  who  have  only  read  this  description  will 
probably  reproach  us  with  having  devoted  ourselves  too 
much  to  details  which  seem  to  them  puerile.  But  we  be- 
lieve that  those  who  have  examined  the  chromatic  sense  of 
a  great  number  of  persons,  and  acquired  thereby  considera- 
able  experience,  will  think  differently. 

"  We  are  convinced  that  time  is  saved  by  such  artifices, 
and  a  more  certain  result  obtained ;  whilst  a  practised  sur- 
geon, who  has  become  to  a  certain  degree  a  virtuoso,  will 
accomplish  his  object  quicker  and  surer  by  such  artifices 
than  one  who  neglects  them.  Recent  experience  fully  con- 
firms this.  All  those  who  have  familiarized  themselves 
with  my  method,  and  have  had  experience  with  color-blind- 
ness, and  of  whose  competence  there  can  be  no  doubt,  report, 
without  exception,  that  it  is  to  be  fully  depended  on,  — the 
most  practical  and  the  best.  Therefore  the  single  unfa- 
vorable opinion  I  know  of  —  namely,  that  of  Dr.  Stilling  ^  — 
can  only  arise  from  neglect  of  the  simplest  rules  of  the 
method.  He  thus  appears  to  have  wholly  overlooked  my 
first  and  most  important  test,  and  admits  his  inability  to 
decide  between  the  names  and  the  color-confusions  of  the 
examined,  which  is  so  readily  done  by  my  method.  ^Moreover, 
he  used  the  ^j/a^e  in  my  book  to  test  for  color-blindness,  in 
direct  opposition  to  my  expressed  directions,  and  the  princi- 
ples of  this  mode  of  trial.  This  will  suffice  to  explain  to 
every  intelligent  person  Dr.  Stilling's  erroneous  and  con- 
fused ideas  as  to  the  application  and  carrying-out  of  my 
method.  The  lack  of  value  of  a  judgment  based  upon  such 
a  misapplication  and  wrong  use  of  the  method  is  self-evident. 

"  An  advantage  of  our  method  we  showed  to  be,  that 
those  who  were  to  be  examined  could  be  present  and  see  each 
individual  tested,  without  this  interfering  in  the  least  with 
the  certainty  of  the  result.  The  individual  test  is  even 
hastened  thereby.  The  color-blind,  and  even  the  normal- 
eyed  who  are  not  familiar  with  colors,  are  generally  rather 
shy  about  being  tested  in  whatever  way  it  is  done.  As  ours, 
however,  is  carried  out,  they  have  more  reliance.  The  ma- 
jority are  even  amused.  The  old  adage  holds  true  here,  that 
it  is  easier  to  find  fault  than  to  do  it  yourself.     The  surgeon, 

1  Die  Priifung  des  Farbensinnes  biem  Eisenbahn  und  Marine- 
personal.    Cassel,  1878, 1st  edition. 


230  COLOR-BLIKDNESS  : 

who  watches  not  only  the  examined,  but  also  those  around, 
can  often  see  from  their  faces  how  closely  the  latter  observe 
the  person  being  tested  when  he  takes  out  the  wrong  colors, 
as  also  when  he  neglects  the  right  ones  under  his  eye.  This 
gives  those  looking  on  confidence  and  assurance,  till  their 
turn  comes,  when  they  appear  as  uncertain  as  before  they 
were  confident.  There  is  in  this  something  attractive,  stimu- 
lating the  interest,  and  hence  not  without  benefit. 

"From  this  we  see  that  our  judgment  of  a  person's  color- 
sense  is  made,  not  only  by  the  material  result  of  the  exami- 
nation, the  character  of  the  worsteds  selected,  but  often  also 
by  the  way  the  examined  acts  during  the  test.  We  should 
mention  a  very  common  manner  of  persons  on  trial,  which, 
in  many  cases,  is  of  great  diagnostic  value.  Often,  in  search- 
ing for  the  right  color,  they  suddenly  seize  a  skein  to  lay  it 
with  the  sample  ;  but  then  notice  it  does  not  correspond, 
and  put  it  back  in  the  heap.  This  is  very  characteristic; 
and,  if  an  examiner  has  often  seen  it,  he  can  readily  recognize 
it,  and  be  assured  that  it  is  an  expression  of  difficulty  in  dis- 
tinguishing the  differences  of  the  colors.  We  frequently 
see  this  in  the  first  test,  with  shades  of  greenish  blue  and 
bluish  green.  Here  it  means  nothing  important :  quite 
the  reverse,  however,  when  it  concerns  the  gray  or  one  of  the 
confusion-colors  1-5.  Uncertainty  and  hesitation  as  to 
these  colors,  which  the  color-blind  do  not  distinguish  from 
the  sample,  even  when  directly  comparing  them,  is  positive 
proof  of  mistake,  implying  defective  chromatic  vision,  like 
the  complete  color-blind.  No  doubt  the  form  of  chromatic 
defect  which  we  have  called  incomplete  color-blindness  exists 
in  several  kinds  and  degrees.  This  is  not  the  place  to  further 
discuss  our  experience  on  this  point ;  and,  for  the  practical 
purpose  we  have  in  view,  it  is  not  necessary.  As  we  have 
explained,  there  are,  among  these,  forms  gradually  approach- 
ing normal  color-sense.  How  they  appear  has  been  described. 
We  designated  them  2^^  feeble  color-sense. 

"  It  is,  perhaps,  not  easy  to  detect  this  special  form  by 
any  other,  or  even  our  own,  method :  therefore  we  give  the 
following  as  a  means  of  so  doing.  The  only  way  of  getting 
at  the  point  is  one  we  gave  in  the  early  chapters  of  our  book; 
namely,  the  determining  at  what  distance  the  examined 
could  distinguish  a  small  colored  surface.     For,  in  fact,  we 


ITS   DANGERS   AND   ITS   DETECTION.  231 

have  to  do  with  a  feeble  color-sense,  which  does  not  prevent 
the  distinguishing  of  the  colors,  but  only  renders  it  difficult. 
We  may  suppose,  in  comparison  to  the  normal  color-sense, 
the  feehle  is  due  either  to  a  weaker  response  to  excitation 
on  the  part  of  the  color-perceptive  organs  of  the  retina,  or  a 
relatively  smaller  number  of  these  organs.  In  either  case 
this  method  would  give  us  the  same  result,  judging  from  our 
experience  in  testing  the  eccentric  portions  of  the  field  of 
vision  with  the  perimeter. 

'-  The  method  we  here  speak  of  shows  us  also  the  effect 
of  habit  and  practice  on  the  color-perception,  and  it  is  worth 
while  to  dwell  on  this  point.  It  happens  not  seldom  that  a 
person  who  by  test  Xo.  I.  has  been  noted  '  incomplete  color- 
blind,' after  they  know  of  their  mistake  and  have  practised 
in  distinguishing  colors,  will  so  comport  themselves  at  a 
second  trial  that  we  have  to  simjDly  mark  them  as  of  'feeble 
color-sense.'  This  fact  might  support  Dr.  Favre's  idea  that 
defective  chromatic  vision  may  be  improved.  This  possi- 
bility, however,  does  not  militate  against  our  hypothesis 
from  the  theory,  as  to  the  nature  of  feeble  color-sense.  It 
does  not  change  our  stand-point  in  the  question.  We  have 
the  same  sometimes  with  test  Xo.  11.,  explainable  by  what 
v\-e  have  said ;  namely,  that,  between  the  complete  lack  of 
chromatic  sense  and  the  incomplete,  there  was  a  series  of 
gradations,  and  that  just  here  practice  would  affect  the  re- 
sult of  examinations. 

"  All  the  examples  here  spoken  of  but  prove  that  many 
seeming  trifles  and  stratagems  are  of  value  in  making  the 
examination,  —  amongst  others  the  keeping  the  sample  a 
little  way  off  from  the  heap  of  worsteds,  as  also  the  removal 
of  every  thing  which  can  cause  the  examined  doubt  and 
uncertainty.  "We  must  not,  therefore,  let  them  do  what 
many  want  to;  namely,  hold  a  number  of  the  worsteds  in 
the  hand  at  once.  We  must  make  the  person'  being  tested 
place  each  skein,  as  he  takes  it  up,  either  with  the  sample 
or  back  on  the  pile.  Many  who  are  not  clear  whether  the 
skein  is  like  the  sample  or  not,  instinctively  put  the  shades 
most  resembling  the  test-sample  at  the  side  of  the  pile 
towards  it,  and  thus  gradually  form  a  little  bridge,  whose 
security  they  would  not  undertake  to  vouch  for.  Xo  such 
half -rules  must,  however,  be  allowed. 


232  COLOE-BLINDNESS  : 


"  Deciding  lolietlier  the  Examined  are  fitted  for  their  Duty. 

"  The  method  of  scrutiny  here  described  is  able  to  detect, 
as  we  have  seen,  not  only  complete  or  incomplete  color- 
blindness, but  a  feeble  chromatic  sense.  Moreover,  it  has 
been  proved  that  there  is  a  perfect  gradation,  from  complete 
color-blindness  on  the  one  side  to  the  normal  chromatic  per- 
ception on  the  other.  The  question  then  naturally  arises, 
from  our  practical  point  of  view,  whether  it  is  possible  to 
draw  a  dividing  line  between  the  kinds  and  degrees  of 
defective  color-vision  which  would  except  those  who  could 
not  cause  any  inconvenience  to  the  railway  service,  and,  in 
case  of  an  affirmative  answer,  where  such  limit  is  to  be 
found. 

"  It  must  first  be  remembered,  that,  in  the  existing  state 
of  things,  these  questions  neither  can  nor  ought  to  be  set- 
tled in  the  same  manner  in  every  case,  since  the  examina- 
tion is  intended  for  individuals  of  two  different  classes,  — 
1st,  the  asj^irants  for  railway  employment;  and,  2d,  the 
employes,  or  those  already  in  service. 

"It  will  be  readily  understood  how  great  is  the  differ- 
ence of  the  cases,  in  deciding  what  may  be  the  result  of  the 
examination.  AVe  have  already  given  our  views  on  this 
point.  Justice  here  calls  for  an  essential  distinction,  sup- 
posing that  the  test  has  been  always  made  with  sufficient 
accuracy.  Hence  we  must  pay  especial  attention  to  both 
of  the  above  classes  when  deciding  whether  an  emj^loye  is 
fitted  for  his  duty. 

"  (A)   Those  who  are  Applicants  for  Railroad  Service. 

"  We  must  bear  in  mind  that  in  Sweden,  according  to 
the  regulation  in  force  there  for  the  management  of  state 
railways  (followed  also,  as  far  as  we  know,  on  the  private 
lines),  it  is  required,  that,  in  order  to  be  admitted,  each 
applicant  '  prove  by  a  certificate  from  a  physician  that  he 
is  exempt  from  any  kind  of  infirmity,  disease,  or  defect  of 
conformation  that  could  be  prejudicial  to  the  exercise  of  his 
functions ; '  and  also,  that  among  these  defects  of  conforma- 
tion, in  connection  with  signals,  are  reckoned  the  defects  of 
the  chromatic  sense,  to  which  the  managers  have  especially 
directed  the  attention  of  the  physicians  attached  to  the 
lines. 


ITS   D^^'GEES   AND   ITS    DETECTION.  Z-Jo 

"  According'  to  the  principles  we  have  stated,  the  greatest 
severity  should  be  observed  in  this  case  ;  or,  in  other  terms, 
the  least  defect  in  the  sense  of  colors  should  be  a  sufficient 
ground  for  rejection. 

"We  must  seek,  therefore,  to  adapt  the  method  of  test  to 
this  law.  The  object  of  a  test  is  to  prevent  any  one  from 
working  as  a  railroad  employe  who  does  not  have  a  perfectly 
normal  color-perception.  We  have  already  sufficiently  ex- 
plained the  evils  arising  from  contrary  action  in  case  of 
»  admission  to  railroad-work.  The  border  between  normal 
and  abnormal  color-sense,  like  that  between  the  normal  and 
abnormal  in  all  analogous  fields,  is  purely  conventional,  and 
can  never  be  sharply  defined.  In  this  case,  however,  it  is 
necessary,  and  our  experience  shows,  that,  so  long  as  the 
question  of  improving  color-blindness  is  an  open  one,  we 
must  consider  as  over  the  border  the  slightest  chromatic 
defect  that  our  method  can  detect,  or  the  slightest  degree  of 
incomplete  color-blindness ;  that  is,  feeble  color-perception. 
In  consideration  of  the  insignificance  of  the  trouble,  our 
demand  seems  hard;  and  yet  we  think  that  it  is  not  too 
severe.  On  the  contrary,  it  is  quite  possible  that  hereafter 
still  stricter  rules  wiU.  become  necessary. 

"  Our  practical  work  is  greatly  simplified  by  drawing 
this  boundary-line.  We  hold  as  fixed  that  the  surgeon  is 
not  to  be  asked  to  decide  whether  a  man  is  fit  for  the  ser- 
vice or  not,  but  simply  to  state  the  kind  and  degree  of  the 
color-blindness  of  the  employe  referred  to  him.  The  de- 
cision of  an  intelligent  person  is  then  immediate  and 
decisive,  whether  he  gives  all  the  examined  a  written  cer- 
tificate, including  the  color-blind,  or  refuses  this  to  the 
latter.  The  statement  of  the  slightest  color-blindness  in 
the  first  case,  as  also  the  refusal  to  give  a  certificate  in  the 
latter,  are  both  equal  to  refusal. 

"  (B)  Employes  already  in  Service. 
"  We  must  here  ask  ourselves  if  we  must  not  modify 
the  limit  we  have  just  traced,  in  order  to  carry  out  the 
principle  we  stated  before  ;  namely,  that  it  is  necessary  to 
adopt  less  severe  rules  as  to  the  elimination  from  the  service 
of  those  who  are  already  employed.  We  here  encounter 
great  difficulties :  and  it  will  be  seen  that  it  is  not  possible 


234  COLOR-BLINDNESS  : 

to  settle  the  question  summarily;  that  is,  that  a  sharply 
defined  limit  cannot  be  traced.  In  such  cases  the  physician 
should  always,  when  he  discovers  a  defect  in  the  chromatic 
sense,  give  a  certificate  which  will  indicate  its  nature. 
These  indications  include,  as  we  have  already  said,  the  di- 
agnoses complete  red-blindness^  complete  green-Umdness,  incom- 
plete color-blindness,  or  a  feeble  cJu-omatic  sense. 

"  Our  method  adheres  strictly  to  the  theory ;  but,  on 
account  of  the  transition-forms,  the  diagnosis  cannot  always 
meet  the  very  exact  demands  of  the  theory.  If  we  class 
with  complete  color-blindness  only  those  cases  in  which  one 
of  the  three  elements  of  the  visual  apparatus  is  wholly 
wanting  or  completely  paralyzed,  and  with  incomplete 
color-blindness  only  those  cases  in  which  none  of  the  three 
are  wholly  wanting,  but  simply  the  receptability  of  one  is 
very  much  reduced,  we  shall  have  to  group  many  cases  of 
the  latter  class  with  the  first.  On  the  other  hand,  we  shall 
often  have  to  consider  the  lower  grades  of  incomplete  color- 
blindness with  feeble  chromatic  sense.  We  must,  however, 
recall  cases  of  a  person  —  especially  if  subsequently  prac- 
tised—  being  at  the  first  examination  marked  as  com- 
pletely color-blind,  whilst  a  second  time  they  appeared  only 
incompletely  color-blind;  and  others  where  a  person  was  at 
one  time  incompletely  color-blind  in  the  fullest  sense  of  the 
word,  whilst  at  another  only  feeble  color-sense  could  be 
shown.  In  such  cases  the  record  should  state,  in  addition, 
'incomplete  color-blindness,'  approaching  complete  red  or 
green,  or  incomplete  color-blindness  of  slight  degree,  &c. 

"  The  same  strict  rule  should  be  applied  to  those  already 
employed  as  to  those  seeking  service,  and  all  discharged 
who  show  any  lack  of  color-perception.  This  would  cer- 
tainly most  surely  protect  the  railroad  service  from  danger. 
Such  a  general  law,  however,  has  its  difficulties,  especially 
as  we  must  recognize,  in  respect  to  the  danger  of  confound- 
ing the  signals,  a  great  difference  between  complete  color- 
blindness and  a  feeble  color-perception.  The  different  cases 
of  incomplete  color-blindness  vary  also  in  degree.  To  draw 
a  line  here,  and  say  beforehand  who  shall  be  dismissed  and 
who  retained,  will  be  as  easy  in  regard  to  the  first  as  diffi- 
cult in  reference  to  the  latter;  for  we  are  convinced  that 
every  case  of  complete  color-blindness  of  both  kinds,  as  well 


ITS   DANGERS   AND   ITS   DETECTION.  235 

as  every  case  of  incomplete  of  the  higher  clegi'ees,  should  be 
immediately  dismissed.  But,  as  regards  those  ^vho  may  be 
retained,  it  is  clear  that  the  first  question  concerns  tliose 
who,  at  the  time  of  the  trial,  were  regarded  in  the  diagnosis 
only  as  having  a  feeble  chromatic  sense,  and  then  those 
who  in  the  first  test  merely  confound  gray  with  the  sample- 
color.  But  we  do  not  venture  to  lay  this  down  as  a  prin- 
ciple; for,  if  it  should  be  proved  that  these  individuals  can 
generally  distinguish  the  light  of  colored  lanterns  with  suf- 
ficient accuracy,  this  does  not  prove  that  it  is  so  in  every 
case,  and  especially  not  at  every  distance  required  in  the 
service.  This  is  why  we  know  nothing  better  to  advise  than 
to  refer  all  such  cases  to  competent  specialists,  as  long  as 
the  transition  period  of  which  we  have  spoken  lasts. 

"  It  may  be  asked,  How  will  the  specialists  themselves 
proceed  ?  To  answer  this,  however,  would  require  a  much 
more  extended  scientific  discussion  of  the  various  methods 
than  we  have  proposed  here  to  make.  We  would  only  give 
some  hints.  A  specialist  who  is  familiar  with  this  subject 
has  all  known  methods  at  his  disposition;  and.  if  these  fail, 
he  need  but  invent  others.  As,  however,  I  have  been  in  the 
position  of  the  specialist  in  reference  to  the  reform  on  the 
railroads  of  Sweden,  I  will  here  say  how  I  have  proceeded. 

"  In  the  examination  of  doubtful  cases  submitted  to  my 
judgment,  I  determined  according  to  several  of  the  methods 
mentioned  in  one  of  the  preceding  chapters.  In  general, 
these  persons  were  all  subjected  to  a  trial  according  to  the 
methods  of  Seebeck  and  Maxwell,  and  an  examination  by 
means  of  the  visual  perimeter  and  of  colored  shadows,  as 
well  as  the  lanterns  of  my  invention  and  colored  glasses. 
These  last  means  have  capacit}'  especially  in  view  ;  and  they 
are  very  suitable  for  the  object,  v,-hen  it  is  desired  to  inves- 
tigate those  who  have  been  already  discovered,  by  miy 
method  of  Berlin  Vvorsteds,  as  having  a  defective  chromatic 
sense. 

"The  light  of  colored  lanterns  and  illuminated  surfaces 
generally,  conveniently  arranged  and  methodically  used, 
may  serve  especially  in  such  cases  to  enlighten  us  as  to  the 
foculty  of  the  person  examined  for  appreciating  colored  sig- 
nals. Our  experiences  of  this  kind  have  shown  us  that  the 
majority  of   color-blind    railway  employes,  however   much 


236  COLOK-BLINDNESS  : 

practice  they  have  had,  are  utterly  incapable  of  recognizing 
and  distinguishing  the  regulation  colors  of  lanterns,  espe- 
cially when  they  are  employed  in  the  shades  which  are  not 
most  commonly  in  use  in  the  service.  This  applies  not  only 
to  the  completely  red  and  green  blind,  but  also  to  the  in- 
completely blind.  These  last  require  the  most  circum- 
stantial investigation,  and  it  is  not  to  be  assumed  that  the 
lower  degrees  can  stand  the  trial.  They  may  often,  it  is 
true,  distinguish  the  signal-lights  at  a  short  distance  with 
sufficient  accuracy ;  but  they  do  not  succeed  at  a  compara- 
tively greater  distance.  As  the  places  where  the  trials  are 
usually  made  do  not  command  such  distances  as  railways 
for  observing  signals,  signal-lights  cannot  of  course  be  used 
for  these  trials.  They  are  replaced  by  small  illuminated 
surfaces,  which,  seen  from  a  suitable  distance,  produce  ex- 
actly the  same  effect  as  lanterns  at  a  great  distance.  Such 
surfaces  are  made  by  placing  a  screen,  with  a  suitable  open- 
ing covered  with  a  colored  glass,  before  the  flame  of  a  lamp. 

"  We  have,  however,  said  enough  in  reference  to  means 
to  be  employed  in  such  cases.  We  had  no  thought  to  enter 
into  the  details  of  them  further,  and  doubt  whether  this 
would  on  the  whole  be  advisable.  The  reason  of  this  will 
be  apparent  from  the  following  chapter." 


ITS   DAXGEES   A2sD   ITS   DETECTION.  237 


CHAPTER   XXI. 

EFFORTS   TO   COXCEAE   OE   TO   FEIGN   COLOE- 
BLIXDXESS. 

"We  have  announced  that  none  of  the  kinds  of  color- 
blindness we  have  in  view  in  this  work  could  escape  dis- 
covery by  our  method.  But  this,  of  course,  assumes  that 
the  subject  does  his  best  in  the  trial,  and  acts  in  good  faith. 
If  it  happen  that  one  persists,  either  in  concealing  a  con- 
scious color-blindness  or  for  some  other  motive,  in  not 
giving  the  least  information  by  act  or  word,  it  is  evident 
that  the  examination  must  fail  from  this  simple  reason,  and 
that  it  is  impossible  to  draw  any  positive  conclusion  with 
regard  to  his  chromatic  sense.  The  examiner  may  in  such 
a  case  mention  unconditionally  in  the  certificate  that  the 
one  examined  refused  to  submit  to  the  usual  examination. 

"  It  is  not  difficult  to  say  how  it  is  necessary  to  act  with 
regard  to  such  persons.  It  should,  in  fact,  be  the  interest 
of  each  one  possessing  normal  sight,  desirous  of  entering 
the  service  of  railways,  kc,  to  endeavor  to  be  competent  in 
every  respect,  and  consequently  to  give  manifest  proof  of 
his  sense  of  colors.  The  color-blind  alone  have  any  inter- 
est in  concealing  their  defect :  therefore  they  endeavor  to 
escape  the  trial.  Every  candidate  who  will  try  to  avoid  the 
prescribed  trial  must  therefore  be  considered  and  treated  as 
color-blind.  Such  obstinacy  on  the  part  of  an  employe 
must  be  considered  and  treated  as  an  infraction  of  the  reg- 
ulations. 

'•But  cases  may  arise  also  in  which  those  possessing  normal 
sight  will  feign  color-blindness,  and  act  as  if  they  were  so 


238  COLOR-BLINDNESS  : 

affected.  This  may  occur  when  some  one  wishes  to  receive 
a  pension  before  the  time,  or  else  to  escape  punishment  con- 
sequent upon  an  unexpected  accident.  These  are  just  the 
very  cases  that  put  the  method  and  perspicacity  of  the  exam- 
iner to  the  test.  ,  The  examination  tlien  assumes  the  character 
of  a  kind  of  criminal  inquest,  where  the  judge  and  the  accused 
must  give  all  the  attention  of  which  they  are  capable  to 
their  reciprocal  acts  and  expressions,  to  try  to  entrap  each 
other.  The  one  examined  tries  to  prove  that  he  is  color- 
blind, while  the  examiner  endeavors  to  prove  that  he  has 
normal  sight.  The  prospect  of  coming  off  victorious  in  so 
singular  a  contest  rests,  in  the  last  resort,  with  him  who  best 
understands  the  nature  of  color-blindness,  and  has  most  ex- 
perience in  the  manner  in  which  the  color-blind  act.  To 
enable  the  pretender  to  deceive  the  examiner,  it  is  absolute- 
ly necessary  that  he  surpass  the  latter  in  knowledge  of 
color-blindness.  There  is  in  this  an  element  of  success  to 
the  examiner,  as  it  would  be  extremely  rare  to  find  a  railway 
employe  or  sailor  who  would,  under  the  circumstances  men- 
tioned, be  subjected  to  an  examination  by  a  person  inferior 
to  himself  in  knowledge.  It  is  clear,  in  fact,  that  an  exam- 
ination so  difficult,  so  minute,  and  involving  so  much  respon- 
sibility, should  be  confided  to  the  most  competent  person 
possible.  But  it  is,  on  the  other  hand,  very  improbable  that 
a  case  should  occur  where  it  would  be  necessary  that  a 
learned  and  experienced  specialist  would  have  to  submit  to 
an  examination. 

"In  the  first  place,  examinations  of  this  kind  must  rarely 
occur;  and,  when  they  do,  it  must  be  at  least  in  the  most 
difficult  cases, — that  is  to  say,  after  an  accident,  —  under 
circumstances  where  the  one  examined'  has  not  had  much 
time  to  study  his  part.  It  will  generally  be  seen  then  that 
he  has  not  a  profound  knowledge  of  the  nature  of  color-blind- 
ness, but  imagines  it  to  be  a  difficulty  or  incapacity  to  dis- 
tinguish signal-colors  or  colors  in  general.  He  will  there- 
fore be  governed  by  this  idea ;  and  either  he  will  perfectly 
distinguish  every  other  color,  so  as  to  mistake  only  the 
signal-colors,  or  else  he  will  believe  he  must  confound  no 
matter  what  color.  But,  as  we  have  seen,  each  kind  of 
color-blindness  follows  laws  as  fixed  as  the  normal  sense. 
Such  a  strategem  will  not  fail  to  violate  them,  and  the  indi- 
vidual will  be  caught  in  the  very  act. 


ITS   DANGERS   AND   ITS   DETECTION.  239 

"  But  there  is  absolutely  nothing  which  opposes  the  sup- 
position that  this  individual  may  have  a  certain  knowledge 
of  the  nature  of  color-blindness,  or,  at  least,  that  he  may 
have  an  idea  of  its  regularity  with  regard  to  the  confusion 
of  colors.  He  may  have  studied  the  proofs  we  have  cited ; 
and,  owing  to  the  exercise  and  observation  of  the  color- 
blind, he  will  know  how  to  perform  them  in  a  manner  suit- 
able to  the  object  in  view.  The  examiner  has  always,  how- 
ever, the  choice  of  other  sample-colors ;  and  the  Berlin- 
worsted  method  affords  a  large  choice.  If  that  does  not 
suffice,  and  the  individual  has  learned  from  the  truly  color- 
blind to  classify  the  whole  collection  of  worsteds  according 
to  their  chromatic  sense,  —  that  is  to  say,  that  he  can  stand 
the  trial  according  to  Seebeck's  method,  —  and  if  he  is  so 
thorough  in  his  part  that  there  is  no  means  of  making  him 
depart  from  it  by  abrupt  or  contradictory  questions,  the  ex- 
aminer may  em-ploy  for  the  examination  a  number  of  other 
known  methods,  but  probably  unknown  to  our  individual.  It 
must  not  be  forgotten  here  that  it  is  generally  easier  to  dis- 
cover faults  committed  by  others,  than  to  avoid  being  guilty 
of  them  one's  self;  and  one  must  be  profoundly  familiar 
with  his  borrowed  part  not  to  be  guilty  of  inconsistencies. 
With  regard  to  feigning  a  certain  kind  of  color-blindness, 
we  know  by  our  experience,  with  regard  to  this,  that  it  is  a 
very  difficult  thing,  and  scarcely  ever  succeeds  before  an 
attentive  and  experienced  examiner.  All  these  circum- 
stances are  advantageous  for  the  examiner ;  but  his  superi- 
ority is  not  limited  to  this.  For  if  it  should  happen  —  an 
extremely  improbable  thing  —  that  a  pretender  were  famil- 
iar with  all  the  known  tests  and  methods,  and  besides  had 
not  less  practice  than  talent  in  executing  them  as  accurately 
as  the  color-blind,  the  examiner  has,  nevertheless,  the  power 
of  inventing,  owing  to  his  special  knowledge,  new  tests,  and 
of  varying  those  already  known. 

"  When  speaking  of  the  examination  of  those  already  in 
service,  and  the  rules  to  govern  us.  here,  we  called  attention 
to  the  necessity  of  acting  with  great  caution  in  doubtful 
cases.  The  test  for  color-blindness  should  then  be  carried 
out  by  a  competent  specialist ;  but  the  details  of  the  several 
methods  he  would  use  we  purposely  omitted.  Still  less  do 
we  think  it  well  to  give  details  in  reference  to  the  trial  of 


240  COLOE-BLINDNESS  : 

those  simulating  color-blindness.  It  rarely  happens  that  a 
writer  or  professor  has  cause  to  withhold  the  very  fullest 
knowledge  of  any  special  department  of  knowledge.  Our 
case  is,  however,  an  exception  ;  for  every  further  detail  is 
but  putting  another  weapon  in  the  hands  of  the  malingerer, 
and  thereby  contributing  to  diminish  the  chances  of  success 
of  the  examining  surgeon.  In  such  case  it  is  not  only  wise 
but  right  to  keep  silence.  It  may  even  be  doubted  whether 
too  much  has  not  already  been  said.  We  thought  it,  how- 
ever, proper  to  say  what  we  have,  in  order  to  convince  others 
that  it  is  very  possible  to  expose  a  malingerer  pretending  to 
be  color-blind.  It  would  be  very  unfortunate  if  the  author 
ities  had  the  slightest  doubt  on  this  point.  It  is  not  im- 
probable that  the  facts  we  have  given  have  caused  one  or 
another  to  give  up  the  difficult  role  of  a^jsewr/o-color-blind. 

"  Of  course  such  examination  requires  the  greatest  care 
and  foresight,  and  must  be  thoroughly  and  perfectly  carried 
out  before  a  decision  is  given.  This  is  justified  by  the  inter- 
ests at  stake.  Although  such  a  test  should  only  be  put  in 
the  hands  of  a  thoroughly  competent  person,  yet  it  is  but 
right  that  a  decision  involving  so  much  (fine  or  imprison- 
ment, perhaps)  should  not  be  left  to  a  single  individual. 

"  Besides  the  precaution,  which  must  not  be  neglected,  of 
conducting  the  examination  in  the  presence  of  expert  and 
competent  persons,  there  is  an  especial  means,  which,  while 
being  certain  of  preventing  all  fraudulent  attempts,  judges 
the  accused  in  the  usual  manner ;  that  is,  by  the  testimony 
of  two  persons.  These  two  witnesses  should  be  two  color- 
blind of  the  same  kind  as  that  feigned  by  the  examined.  If 
these  two  individuals  are  first  subjected  separately  and  in- 
dependently of  each  other  and  the  pseudo-co\ov-h\\i\d.  to  the 
same  trial  as  he,  let  the  results  be  noted  down  carefully,  and 
then  the  whole  three  together ;  and  it  will  then  soon  be  seen 
how  the  case  stands  with  the  suspected  individual.  The 
two  color-blind  will,  in  this  manner,  give  the  necessary  tes- 
timony without  resting  upon  the  discretion  of  the  examiner. 
This  manner  of  proceeding  must,  however,  be  employed  with 
caution  and  discrimination,  as  the  conformity  between  two 
color-blind  of  the  same  class  is  not  absolutely  perfect  in 
every  resi^ect.  The  result  must  therefore  always  be  made 
to  harmonize  by  the  explanation  of  the  examiner." 


ITS  DAKGEES   AXD   ITS   DETECTION.  241 


CHAPTER  XXII. 

METHOD  OF  DECIDING  THE  PKECISE  AMOUNT  OF 
COLOR-BLINDNESS  BY  HOLMGBEN's  CHEOMA- 
TOSKIAMETER,  OR  COLOR-SENSE  TESTER.  —  PRO- 
FESSOR DONDERS'S  INIETHOD  OF  DETERMINING 
QUANTITATIVELY  COLOR-PERCEPTION. 

One  of  the  additional  methods  of  detecting 
color-blindness  is  of  value  for  examiners  to  be 
acquainted  with.  It  is  based  on  the  true  principle 
of  comparison,  no  names  of  color  being  required 
of  those  examined.  It  also,  like  the  method  of 
Bonders,  enables  us  to  express  in  figures  the 
amount  of  the  chromatic  defect  in  each  individual 
case.  The  apparatus  is  arranged  to  enable  us  to 
use  colored  shadows.  It  is  not  very  expensive, 
and  can  be  used  by  day  or  night.  To  further  test 
railroad  employes  or  others,  after  having  decided 
on  their  color-blindness  by  Holmgren's  worsteds,  it 
will  be,  as  I  said,  of  great  value  to  examiners, 
and  also  serve  the  purpose  of  physiological  experi- 
menters. It  has  the  advantage  of  giving  constant 
results  independent  of  the  examiner.  These 
results  can  be  readily  understood  by  the  laity, 
and  the  test  applied  before  them.     As  Professor 


242  COLOR-BLINDNESS  : 

Holmgren  says,  "  the  apparatus  may  also  be  used 
in  determining  the  absorptive  power  of  various 
colored  glasses,"  &c.  It  must  be  understood  that 
it  is  a  means  or  method  for  the  expert  alone 
to  employ.  I  will  here  give  the  author's  full  de- 
scription of  it.  He  has  tested  it  thoroughly  with 
the  many  color-blind  found  on  the  railroads  and 
elsewhere  in  Sweden.  It  is  not  described  in  his 
book,  and  first  appeared  in  a  pamphlet  in  Swedish. 
The  following  is  from  a  condensed  description  in 
German,  given  by  Professor  Holmgren  himself:  — 

"  I  would  devote  a  special  chapter  to  the  discussion  of  the 
conditions  of  colored  shadows,  and  the  importance  of  the  light 
by  which  they  are  produced.,  I  have  found  it  very  difficult, 
if  not  impossible,  to  get  a  shadow  which  reflects  no  light. 
Without  light  the  shadow  in  simultaneous  contrast  has  no 
color. 

"  I  hold  here  also,  as  always,  that  every  method  for  the 
detection  of  color-blindness  mu§t  depend  on  the  principle  of 
cojnpar'ison  of  different  colored  lights  or  surfaces.  In  this 
sense  the  colored  shadows  can  be  used  as  any  other  colored 
surfaces  if  they  are  produced  by  two  lights,  or,  what  amounts 
to  the  same,  by  two  from  the  same  source.  We  may  thus 
use  the  light  of  a  single  lamp,  by  letting  one  portion  pass 
through  the  colored  glass  to  the  object  causing  the  shadow, 
and  the  screen  on  which  the  shadow  is  cast;  whilst  another 
portion  of  the  light,  by  means  of  a  mirror  near  the  glass,  is 
thrown  upon  the  same  object.  \\q  thus  have  two  shadows 
on  the  screen  of  comx3lcmentary  color.  One  is  illumined 
alone  by  the  light  through  the  colored  glass,  the  other  wholly 
by  the  light  of  the  lamp  reflected  from  the  mirror ;  whilst  the 
rest  of  the  surface  of  the  screen  is  illuminated  by  both.  Now, 
as  we  move  the  mirror  to  or  from  the  lamp,  we  can  regulate 
the  relative  luminosity  of  the  shadows.  I  have  constructed 
such  an  apparatus,  which  I  would  call  a  chromatoskiameter. 
hi  the  centre  of  the  apparatus  is  a  petroleum-lamp  with  a 
round  wick.  The  lamp  is  on  a  stand,  from  which  project  two 
horizontal  movable  arms.    On  these  arms  are  the  rest  of  the 


ITS   DANGERS   AND  ITS  DETECTION.  243 

appamtus.  The  colored  glass,  the  pencil  to  cast  the  shadow, 
and  the  screen  of  -U'hite  porcelaine  on  vrhich  the  shadow  is 
cast  are  arranged  on  one  of  these  horizontal  arms  at  a  fixed 
distance  from  the  flame.  On  the  other  arm  is  the  mirror 
which  can  be  moved  to  or  from  the  lamp.  The  arms  are 
marked  on  the  sides  with  a  millimetre  scale,  supposed  to 
commence  in  the  centre  of  the  flame.  Thus  the  distance  of 
the  several  parts  from  the  lamp  can  be  read  off  on  the  scale. 
"  In  employing  the  instrument,  I  have  used  a  red  glass, 
which  allowed  only  spectral  red  to  pass,  and  a  green,  which 
passed  mostly  the  middle  spectral  green,  but  also  some  other 
light,  —  no  red,  however.  In  using  the  instrument  to  detect 
color-blindness,  we  must  grade  it  by  trial,  and  determine  its 
constants  for  the  glass  used.  We  must,  for  this  purpose, 
find  for  each  glass  the  distance  the  mirror  must  be  from  the 
flame  to  cause  the  two  shadows  to  appear  alike  to  the  nor- 
mal eye  ;  that  is,  of  the  same  degree  of-  brightness  each  of 
its  own  color.  This  distance  of  the  mirror  for  my  eye  I 
found,  for  the  red  glass,  to  be  40  centimeters ;  for  the  green, 
35  centimetres,  —  a  difference  of  5  centimetres.  To  find 
this  position  of  the  mirror  is  much  easier  with  the  color- 
blind than  the  normal-eyed,  for  the  simple  reason  that 
for  the  former,  v/hen  the  shadows  are  of  the  same  degree  of 
brightness,  they  are  generally  of  the  same  color.  The  dis- 
tance of  the  mirror  for  him  is  quits  different  from  that  of 
the  normal-eyed,  and  so  characteristic  as  to  detect  him 
thereby.  It  is  also  very  different  in  different  cases.  All 
the  cases  examined  can  be  separated  into  two  distinct  series, 
corresponding  to  the  two  forms  of  color-blindness  I  have 
described ;  namely,  red-blindness  and  green-blindness.  The 
distance  of  the  mirror  with  red-blindness  (the  average  of 
25  cases)  was,  — 

For  the  red  glass    •  =      73.2  centimetres 

For  the  green  glass  =      27.6  " 

Difference  (R.  G.)   ==      45.G  centimetres 
With  green  blindness  (from  an  average  of  35  cases  recorded) 
the  distance  of 

The  green  glass  was  =      48.5  centimetres 

The  red  glass  was      =      28.7      -    " 

Difference  (Gr.  R.)  =      19  8  centimetres 


244  COLOE-BLINDNESS  : 

"  Incomplete  color-blindness  may  also  readily  be  detected 
by  differences  of  the  mirror's  distances  from  that  for  the 
normal  eye.  For  the  very  slightest  grades  of  chromatic 
defect  this  method  is  not  so  good  to  be  used  alone,  since 
such  forms  of  the  trouble  are  apt  to  be  confused  with  a  lack 
of  knowledge  or  understanding  in  reference  to  appreciating 
the  relative  luminosity  of  the  shadows. 

"  In  the  original  article  the  examination  of  135  cases 
of  various  grades  of  color-blindness  was  recorded.  This 
method,  as  is  seen,  is  based  wholly  on  the  principle  of  com- 
parison. It  is  not,  however,  the  comparison  of  two  colors, 
but  that  of  the  intensity  of  two  lights  of  different  kinds.  It 
has  this  practical  advantage,  that  the  color-blind,  who  are 
very  sensitive  to  differences  of  luminosity,  can  readily  find 
the  right  position  of  the  mirror.  Theoretically  there  is  also 
the  advantage  that  it  shows  the  chromatic  defect  to  be  a 
lessened  sensitiveness  for  a  special  kind  of  light, — one  of 
the  primary  colors. 

"  In  the  respective  distances  of  the  mirror  from  the  flame, 
as  read  off  from  the  scale,  compared  with  the  distance  for  the 
normal  eye,  we  have  in  every  case  a  relative  measure  of  the 
reduced  sensitiveness.  Now,  as  the  mirror  is  movable,  and 
can  be  altered  in  position  till  the  luminosity  of  the  two 
shadows  is  alike  to  the  eye  of  the  person  examined,  the 
intensity  of  the  unaltered  lamp-light  on  one  shadow  will 
serve  to  measure  the  intensity  of  the  light  on  the  other 
shadow,  which  has  passed  through  the  colored  glass,  and 
become  more  or  less  homogeneous.  As  the  zero-point  of 
the  scale  is  in  the  flame,  greater  numbers  or  distances  of  the 
mirror  must  corresjoond  to  lessened  sensibility  to  light  of 
the  color  of  the  glass.  This  quite  agrees  with  the  numbers 
above  given  for  red  and  green  blindness;  the  first  showing 
abnormal  w^ant  of  sensitiveness  for  red,  and  the  latter  for 
green  light.  This  agrees  again  with  the  Young-Hemholtz 
theory,  and  also,  as  w^ell,  with  the  results  of  my  tests  with 
the  worsteds.  The  cases  referred  to  were  first  tested  with 
the  worsteds,  and  the  diagnosis  confirmed  by  examination 
with  the  chromatoskiameter. 

"  The  characteristic  confusion  of  colors  of  the  color-blind 
does  not  necessarily  imply  a  great  reduction  of  perception 
for  any  one  of  the  primary  colors.     They  are  explainable  by 


ITS   DANGERS   AND   ITS   DETECTION.  245 

a  disturbance  of  the  color-sense  in  the  individual  case, 
whereby  the  sensibility  for  one  of  the  primaiy  colors,  inde- 
pendently of  its  real  value,  is  reduced  in  comparison  with 
sensibility  of  the  other  two.  This  explains  a  large  number 
of  the  cases  tested  with  this  instrument.  Hence  it  is  of 
value  to  test  each  case  with  two  complementary  colored 
glasses.  The  difference  between  the  distances  of  the  mirror 
for  each  expresses  the  value  of  the  defect  to  be  ascertained. 

"  The  absolute  distance  of  the  mirror  has  of  course  only 
a  relative  value,  does  not  immediately  represent  the  intensity 
of  the  illumination  of  the  shadow ;  that  is,  the  sensitiveness 
of  the  eye  examined.  This,  however,  w^e  can  deduce  from 
a  formula  I  will  here  give.  Taking  the  above  figures  as 
representing  the  average  distance  of  the  mirror,  the  sensi- 
tiveness of  the  normal  eye  (the  intensity  of  the  lamp  being 
unity) 

For  the  red  light      =  0.115. 

For  the  green  light  =  0.137. 

The  average  sensitiveness  of  the  red-blind 

For  red  light  =  0.048. 

The  average  sensitiveness  of  the  green-blind 

For  green  light  =  0.088. 

Or,  if  we  regard  the  normal  color-sense  as  a  measure  for 
the  sensitiveness, 

Normal  color-sense  =  1.00. 

Eed-blindness  =  0.42  (R.). 

Green-blindness       =  0.64  (Gr.). 

By  the  value  gained  from  the  distance  of  the  mirror,  applied 
to  normal  color-sense,  we  may  calculate  the  absorptive  power 
of  the  glass.  The  absorption  by  the  glass,  expressed  as  loss 
of  light,  is  thus  :  — 

For  the  red  glass      =  42.5  centimetres. 

For  the  green  glass  =  43.1  centimetres. 

"  Thus,  by  using  a  larger  number  of  suitable  colored 
glasses,  we  can  study  not  only  the  normal  chromatic  sense, 
but  also  the  various  forms  of  color-blindness.  The  princi- 
ple of  the  method  does  not,  however,  restrict  us  in  practice 
to  colored  shadows  ;  but  it  may  be  extended  to  any  colored 


246  COLOP.-BLINDNESS  : 

lights  or  surfaces.  Therefore  it  would  be  well,  upon  the 
same  principle,  to  employ  the  spectral  light  in  the  study  of 
the  color-sense  and  its  defects. 

"  I  have  here  confined  myself  to  the  use  of  two  glasses, 
principally  because  these  experiments  were  directed  to  the 
detection  of  color-blindness  among  the  personnel  of  the 
Swedish  railroads,  where,  of  course,  we  were  concerned 
with  the  red  and  green  only.  These  examinations  have  at 
least  proved  the  existence  of  green-blindness  as  an  inde- 
pendent typical  species,  in  accordance  with  the  Young- 
Helmholtz  theory,  hitherto  but  little  regarded,  or  ignored. 
This  is  directly  opposed  to  the  idea  that  red  and  green 
blindness  are  but  one  and  the  same  thing,  called  red-green- 
blindness. 

"  As  to  the  practical  use  of  this  method,  I  regard  it  only 
as  one  of  the  category  I  have  called  methods  of  control,  and 
in  my  original  article  have  given  the  reasons  why  it  is  not 
comparable  with  my  worsted  method  as  a  preliminary  test, 
which  I  still  regard  as  the  best  of  any  at  present  proposed." 

Another  method  of  quantitative  determination 
of  color-blindness  was  carried  out  by  Professor 
Bonders  on  the  Holland  railroads.  It  has  not 
been  given  in  English,  and  I  present  it  for  the 
benefit  of  our  examiners  in  this  country.  Like 
this  one  of  Holmgren's,  it  is  an  additional  method. 

PROFESSOR   DONDERS'S   METHOD    OF    QUANTITATIVELY 
DETERMINING    COLOR-PERCEPTION. 

"  Approaching  slowly  a  small  colored  object,  the  normal 
eye  detects  the  color  but  little  later  than  the  light.  We 
shall  not,  however,  seek  long  before  finding  a  person  who 
sees  the  color  much  later  than  he  sees  the  light.  On  this 
is  based  my  method  of  examination. 

"  For  testing  with  reflected  light,  disks  of  colored  paper 
are  used,  1,  2,  5,  or  more  millimetres  in  diameter.  Each 
one  is  separately  glued  to  a  little  piece  of  black  velvet ; 
and,  in  like  manner,  pieces  from  the  white,  red,  and  green 
signal-flags.  These  little  pieces  of  velvet,  with  the  colored 
disks  on  them,  can  with  slight  pressure  be  made  to  adhere 


ITS   DAXGEES   AXD   ITS   DETECTION.  247 

to  a  larger  piece  of  velvet  a  metre  square,  fastened  upon  the 
wall,  and  on  vrbich  one  or  more  can  thus  be  exhibited  as 
we  desire. 

"  Color-perception  K  is  in  the  inverse  proportion  to  the 
amount  of  light ;  that  is,  equal  to  the  square  of  the  distance 
(/,  at  which  the  colors  are  recognized,  and  inversely  propor- 
tional to  the  square  of  the  diameter  m.  Let  D  represent 
the  distance  at  which  the  normal  eye  sees  color,  of  m  =  1 
(that  is,  disks  of  one  millimetre  diameter),  and  we  have 

^  —  rrt2  '  1)2" 

This  formula  gives  for  the  normal  eye  K  =  1,  and  for  every 
other  eye  K  <C  1. 

"In  the  formula  of  visual  acuteness  Y  =  yj,  the  distances 
are  simply  d  and  D  (not  d-  and  D-),  because  the  distinguish- 
ing a  printed  letter  is  in  proportion  to  the  visual  angle  in 
all  directions.  Moreover,  in  this  formula  D  is  regarded  as 
constant.  This  is  because,  in  the  varying  light  of  an  ordi- 
nary room,  with  fair  light,  the  visual  power  is  near  its 
maximum.  This  does  not  hold  in  the  same  degree  in  refer- 
ence to  distinguishing  color.  The  lack  of  light  is  of  course 
partly  compensated  for  by  the  greater  sensibility  of  the 
retina  and  the  wider  pupil ;  but,  with  increasing  daylight, 
the  perception  of  most  colors  also  increases  very  consider- 
ably. Therefore  it  is  important  for  the  examiner  to  deter- 
mine each  time  his  own  D,  and  take  this  into  consideration. 
In  deciding  the  visual  acuteness  (form-perception),  we  take 
into  account  diminished  illumination  when  it  materially 
reduces  our  own  visual  power.  This  is  all  the  more  neces- 
sary with  color-perception,  since  the  same  colors  are  not  to 
be  obtained  exactly  alike  everywhere  ;  and  those  .obtainable 
are  not  always  recognized  at  the  same  distance.  Moreover, 
from  use  they  lose  their  brightness.  We  may,  however, 
accept  as  a  general  law,  that  bright,  saturated  colors,  one 
millimetre  in  diameter,  when  placed  on  black  velvet  in  a 
good  light,  will  be  seen  by  an  eye  with  normal  visual  acute- 
ness (ametropia  being  corrected)  at  a  distance  of  Jive 
metres. 

'•This  method  supposes  that  the  examiner  has  normal 
color-sense,  which  is  readily  determined  by  comparison  with 
others.     It  is  also  necessary  that,  before  testing,  both  the 


248  COLOE-BLINDNESS  : 

examined  and  examiner  should  have  been  in  the  room  for 
a  time  with  equal  illumination.  Decreasing  daylight  re- 
duces all  colors,  but  not  all  equally.  Blue,  for  instance, 
requires  of  all  the  colors  the  least  light  to  be  recognized 
when  we  pass  from  a  darker  to  a  lighter  locality ;  the  most 
light,  on  the  other  hand,  when  we  go  from  a  lighter  to  a 
darker  locality. 

"  For  transmitted  light,  the  flame  of  a  candle  may  be 
used,  such  as  is  employed  in  England  to  determine  the 
candle  power  of  gaslight.  This  is  placed  behind  a  black- 
ened wooden  screen,  in  which  is  an  opening,  25  mm.  in 
diameter,  covered  with  ground  glass.  In  front  of  this  hole 
a  rotating  metal  disk  is  arranged,  pierced  with  holes,  1,  2, 
6,  10,  and  20  mm.  Just  behind  the  opening  in  the  screen 
is  a  rotating  disk  with  holes,  —  one  clear,  the  others  contain- 
ing red  and  green  signal-lantern  glass,  as  also  other  colors, 
which  we  can,  by  turning,  bring  in  front  of  the  hole  in  the 
screen.  The  candle  is  arranged  to  slide  along  a  scale, 
thereby  giving  us  its  distance  from  the  screen.  The  red 
glass  is  one  that  passes  mostly  red  rays,  up  to  orange,  but 
no  others.  The  green  is  one  which  passes  a  part  of  the 
rays  from  yellow  to  bluish  green,  and  a  little  of  the  red. 

"  During  the  examination,  daylight  is  to  be  so  far  ex- 
cluded from  the  room  as  to  only  render  recognition  possible 
close  to.  We  can  then  determine  the  distance  A,  at  which, 
for  the  normal  eye  for  white  and  colored  light,  with  m  =  1, 
D  =r  5  metres.  At  this  distance  D  in  the  formula  will  keep 
the  nearly  constant  value  of  5  metres. 

"  With  the  candle  and  the  finely  ground  glass  employed, 
the. white  candle-light  will  give  us  A  =  1.75  metres,  the 
red  glass  will  give  us  A  =  0.65  metres,  the  green  A  =  0.25 
metres.  In  this  test  with  transmitted  light,  care  must  be 
taken  to  keep  the  opening  in  the  direction  of  the  candle. 
The  examination  is  otherwise  conducted  in  the  same  way 
as  with  reflected  light.  If  the  examined  is  color-blind, 
then  the  degree  of  brightness  for  the  several  colors  is  not 
the  same  in  respect  to  A,  and  they  decide  the  color  from 
this  difference  in  the  brightness.  This  is  shown  if  we  vary 
the  value  of  a,  when  those  who  are  uncertain  call  the  color 
alternately  red  or  green.  When  using  the  largest  opening, 
and  bringing  the  flame  close  to  the  glass,  there  are  but  few 


ITS   DANGERS   AND   ITS   DETECTION.  249 

persons  who  fail  in  recognizing  the  color  if  close  to.  In 
this  numerical  determination  to  also  decide  the  recognition 
with  stronger  illumination,  we  need  only  make  our  formula 

-Tg,  where  a  is  the  distance  of  the  flame  from  the   glass 

found  necessary,  and  A  its  normal  distance.  The  power  of 
color-perception  will  then  be 

i    ^    ^ 


^         -  -  /I    d      a\ 


\     d     a 

Taking  V  K  =  ~' j)'  -t=^,  it  follows,  as  L  is  found  by 

observation,  that  the  power  of  color-sense  K=:L2.     It  is 
more  practical  to  hold  to  JL,  and,  in  general,  to  remember 

L  =  V^.     With  reflected  light  -r  is  eliminated,  and,  with 

transmitted  light  generally,  a  =  A ;  so  that,  as  a  rule,  we 

,  Id 

may  confine  ourselves  to  the  formula  L  r=  -  •  y^,  and,  if  we 

use  the  one  millimetre  opening,  to  the  formula  L  =  ^. 

"  It  is  interesting  to  observe  how  the  examined  gradually 
passes  from  doubt  to  certainty.  "We  show  him  a  single  test 
at  five  metres'  distance.  He  sees  the  little  disk,  but  not  its 
color.  A  step  nearer,  and  he  ventures  to  call  it  "red." 
Another  step,  and  he  doubtfully  says,  "No,  green."  Finally, 
he  says  "  red  "  again,  and  at  last  decides  more  positively  for 
this  color.  Just  where  he  became  certain  is  readily  deter- 
mined. Or  we  put  a  number  of  the  disks  of  varying  diame- 
ters together  on  the  large  piece  of  velvet,  and,  pointing  to 
each  with  a  stick,  ask  its  color  quickly.  With  partial  color- 
sense  it  readily  appears  how,  in  approaching,  first  the  larger 
disks,  and  then  the  smaller,  are  rightly  named;  whilst  with 
less  color-perception  only  the  larger  are  told  close  to,  and 
where  there  is  complete  absence  the  color  of  even  these  is 
not  recognized.  We  may  thus  determine  the  numerical 
degree  of  color-blindness  with  sufiicient  accuracy. 

"  The  disk  must  not  be  steadily  gazed  at.  The  examined 
must  turn  his  eyes  aside,  and  step  nearer,  at  once  giving  the 
uame  of  the  color  pointed  out.  If  the  answer  is  not  imme- 
diate, then  again  a  step,  with  the  eye  removed  from  the 


250  COLOR-BLINDNESS  : 

object,  and  the  question  repeated.  By  steady  gazing,  the 
complementary  color  may  be  called  up  in  the  eye,  and  the  de- 
cision rendered  difficult." 

In  a  letter  to  me  of  Feb.  23,  1879,  Professor 
Bonders  says,  — 

"  I  think  I  may  have  given  too  brief  a  description  of  my 
method.  Dr.  Daae  did  not  understand  that  it  was  not  the 
preliminary,  but  only  the  secondary,  examination  in  which 
transmitted  light  was  used,  and  where  the  distinction  of 
colors  had  already  been  proved  imperfect.  Dr.  Stilling 
says,  that,  continuing  to  fix  the  eye  on  the  disk,  the  second- 
ary image  of  complementary  col^r  is  developed,  not  aware 
that  I  expressly  said  that  I  allow  only  one  or  two  seconds 
for  giving  the  name  of  the  color.  Others  speak  of  the  great 
difference  of  the  daylight,  and  forget  that  I  prescribe  that 
every  observation  is  to  be  made  at  the  same  time  by  the 
examined  and  the  examiner,  the  latter  noticing  at  what 
distance  (indicated  at  the  point  where  the  examined  sets  his 
foot)  he  distinguishes  the  color ;  and,  if  this  is  not  five  metres, 
then  it  is  to  be  put  in  the  formula  as  four  or  three,  or  what- 
ever distance  it  is  found.  The  determination  or  calculation 
is  not  thereby  rendered  longer  or  more  difficult." 

I  considered  it  proper  to  introduce  here  Professor 
Donders's  replies  to  the  criticisms  made  on  his 
method,  since,  as  we  see,  they  arose  from  a  misun- 
derstanding, or  neglect  of  his  "iirections  for  con- 
ducting this  quite  practical  test,  and  which  was 
carried  out  on  the  Holland  roids,  as  I  have  for- 
merly described.  I  also  give  the  whole  explana- 
tion of  the  test,  as  it  is  the  one  required  to  be  used 
at  present  by  the  five  ophthelmic  surgeons  now 
authorized  to  examine  candidates  for  railroad  ser- 
vice in  Holland. 


ITS   DANGEHS   A^^D   ITS   DETECTION.  251 


CHAPTER  XXIII. 

LAWS  OF  CONTROL  OF  COLOR-BLINDNESS  NOW 
IN  FORCE  IN  EUROPE.  —  LEGISLATIVE  ACTION 
OF   THE   STATE   OF   MASSACHUSETTS. 

Here  in  the  United  States,  either  the  several 
State  legislatures,  the  State  railroad  commission- 
ers, or  the  individual  railroad  corporations,  will  be 
sooner  or  later  called  upon  by  the  community  to 
establish  and  carry  out  some  regulations  control- 
ling color-blindness  among  the  employes :  there- 
fore it  becomes  of  considerable  importance  for  all 
parties  interested  to  know  how  this  control  has 
been  effected  in  Europe,  and  the  precise  manner  of 
conducting  the  test.  In  order  to  answer  this,  I 
have  corresponded  with  many  surgeons  in  Europe, 
and,  through  their  instrumentality,  am  able  to  here 
give  the  at  present  provisional  laws  in  reference 
to  most  of  the  European  states. 

The  European  governments  have  not  stopped  to 
frame  laws,  but  immediately  carried  out  the  exam- 
inations, and  are  subsequently  considering  the  pre- 
cise regulations  for  the  future,  &c.  It  will  be  also 
seen  that  the  governments  have  provided  for  the 
elimiDation  of  all  color-blind  from  their  own  rail- 
roads and  navies.     The  private  companies,  where 


252  COLOR-BLINDNESS: 

independent  of  their  government,  have  followed 
its  action.  In  what  I  have  to  say  as  to  these  laws, 
&c.,  there  is  much  of  vital  importance  for  us  in 
the  United  States  about  to  commence  this  control. 
I  would  call  the  especial  attention  of  mj  readers 
to  the  prudent  and  practical  action  of  the  Swedish 
Government,  in  comparison  with  that  of  the  Ger- 
man states,  in  putting  at  the  head  of  the  control 
one  who  was  as  competent  to  conduct  it  as  he  was 
to  originate  the  method  of  testing. 

Professor  Holmgren  kindly  furnishes  me  the 
following  in  reference  to  Sweden :  — 

CIRCULAR    OF    THE   ROYAL  SWEDISH   RAILROAD  DIRECTORY 
TO    THE    SUPERINTENDENTS. 

To  the  Superintendents. 

The  royal  directory  would  hereby  call  the  attention  of 
the  respective  district-surgeons  to  the  fact  that  the  lack  of 
power  to  distinguish  the  several  primary  colors  excludes 
entrance  to  raib'oad  service :  therefore  persons  seeking 
service  must  be  tested  for  any  such  lack  of  visual  power. 

As  it  is  of  importance  to  be  assured  that  the  officials  now 
in  service  can  distinguish  correctly  the  colors  used  in  sig- 
nals, the  chiefs  of  sections,  by  means  of  the  usual  flags  and 
lanterns,  or  other  means  they  may  find  best  adapted,  are  to 
ascertain  if  those  under  them  are  incapable  of  recognizing 
these  colors.  The  results  of  such  examinations  are  to  be 
reported  to  the  directory,  and  any  suggestions  in  reference 
to  dismissals  which  may  seem  necessary. 

Surgical  assistance  will  not  be  necessary  with  this  last- 
named  trial. 

C.  O.  Troilius. 

C.    LiMNELL. 

Stockholm,  Sept.  16,  1876, 

Professor  Holmgren  writes  me,  — 

"  Having  called  the  directory's  attention  to  the  fact  that 
these  rules  in  reference  to  those  already  in  service  were  not 


ITS   DANGERS   AND   ITS   DETECTION.  253 

sufficient,  but  that  a  thorough  examination  by  the  railroad- 
gurgeons  should  be  made,  for  which  the  surgeons  must  learn 
my  method,  the  following  circular  was  issued :  — 

CIRCULAR. 

To  the  Superintendents  of  all  the  Districts. 

The  directory  hereby  orders  a  surgeon  from  each  district, 
next  Tuesday  the  24th  at  12  m.,  to  meet  Professor  Holmgren 
in  Upsala,  to  there  learn  from  him  his  method  of  testing  for 
color-blindness  among  the  employes.  __  Any  other  of  the  sur- 
geons of  the  district  may  also  attend  the  professor  at  this 
time  for  the  same  purpose. 

A  pass  is  to  be  issued  both  to  those  surgeons  who  are 
sent  to  this  meeting,  and  to  those  who  desire  to  attend,  in 
accordance  with  the  seventh  clause  of  the  travelling  regula- 
tions. 

CO.  Troilius. 

C.    LlM2sELL. 

Stockholm,  Oct.  16, 1876. 

To  the  Superintendents. 

Since,  in  accordance  with  the  directions  of  Sept.  16,  1876, 
a  number  of  the  railroad-surgeons  have  learned  from  Pro- 
fessor Holmgren  his  method  of  examination  for  color-blind- 
ness, the  directory  hereby  prescribes, 

That  this  examination  shall  be  gradually  carried  out 
among  the  TQA\ro2i(\.  personnel  by  the  surgeons,  in  accordance 
with  Professor  Holmgren's  method. 

That  the  surgeons  who  may  not  have  already  learned 
this  method  shall  instruct  themselves,  either  directly  from 
Professor  Holmgren  himself  in  Upsala,  or  through  those 
who  attended  his  lecture  on  this  subject. 

That  they  report  to  the  directory  the  result  of  their  ex- 
aminations, together  with  such  suggestions  as  were  required 
by  the  circular  of  Sept.  16 ;  and,  when  color-blind  are  found 
in  positions  where  the  distinguishing  the  colors  is  important, 
they  are  to  immediately  make  the  necessary  reports  and  re- 
marks which  the  circumstances  require,  without  waiting  the 
termination  of  the  tests. 

C.  O.  Troilius. 

C.    LiMXELL. 

Stockhol:m,  Nov.  9, 1876." 


254  COLOK-BLINDNESS  : 

The  directions  of  the  superintendents  to  the 
surgeons  were  as  follows,  for  an  example :  — 

To  Railroad-Surgeon  Professor  C    B.  Merterton,  Upsala. 

The  following  from  the  di  -ections  of  the  royal  railroad 
directory  is  communicated  foi  your  information  and  govern- 
ment :  — 

That  the  railroad-surgeor  s  are  to  test  all  employes  for 
color-blindness  by  Professor  flolmgren's  method. 

That  those  surgeons  who.  may  not  be  acquainted  with 
this  method  are  to  at  once  inform  themselves,  either  from 
Professor  Holmgren  in  Upjala,  or  from  some  of  the  sur- 
geons who  have  heard  his  e  splanations  and  lecture  on  the 
subject. 

That  a  report  of  these  examinations  is  to  be  made  as 
soon  as  possible. 

In  reference  to  the  personnel  of  the  traffic-department 
now  employed,  all  station-masters  have  orders  to  transmit 
you  lists  of  the  whole  jjersonnel  under  them;  and  you  are  to 
record  in  the  proper  columns  such  remarks  as  the  examina- 
tion calls  for. 

C.  J.  Hemmarskord. 

Stockholm,  Superintendent's  Office 

of  the  Fifth  Traffic  District,  Nov.  13, 1876, 

"  This  is  all  official  which  relates  to  the  railroads.  It  is, 
however,  seen  that  all  necessary  is  practically  accomplished. 
1st,  Those  entering  the  service  must  be  tested  for  color- 
blindness, and  all  showing  the  slightest  lack  of  color-per- 
ception refused.  2d,  All  those  now  employed  are  to  be 
tried,  and  the  color-blind  either  dismissed,  pensioned,  or 
given  employment  where  the  recognition  of  the  colored 
signals  is  not  necessary.  I  have  acted  as  chief  of  control, 
and  tested  over  again  all  those  who  were  found  defective  by 
the  railroad-surgeons. 

"  You  will  thus  see  we  have  been  very  practical.  With- 
out first  making  any  laws,  we  carried  out  the  reform  quite 
simply  under  my  personal  supervision.  I  still  act  as  the 
head  of  the  control  of  color-blindness;  and,  now  that  we 
have  gained  a  thorough  practical  experience,  we  shall  this 
year  establish  laws  to  govern  the  railroads  and  the  marine." 
(In  letter  of  January,  1879,  of  Professor  Holmgren  to  me.) 


ITS   DANGERS   AND   ITS   DETECTION.  255 

The  Swedish  navy  and  mercantile  marine  have 
not  been  neglected ;  and  I  will  here  give  a  tran- 
script from  the  laws  in  reference  to  the  former,  as 
prepared  by  Professor  Holmgren.  In  reference  to 
the  mercantile  marine,  Professor  Holmgren  writes 
me  of  date  March  5,  1879:  ^'I  have  been  unable 
as  yet  to  forward  j'ou  the  laws  concerning  the  con 
trol  of  color-blindness  in  the  merchant  marine. 
The  government  has  not  yet  given  its  sanction. 
They  are  thorough,  definite,  and  strict."  It  must 
be  remembered  that  all  these  laws  of  Sweden  and 
the  other  European  countries,  as  here  given,  must 
be  considered  as  only  provisional,  and  to  simply 
serve  the  present  purpose  of  immediately  carrying 
out  the  test  and  the  control  of  color-blindness. 

ORDERS  IX  REFERENCE  TO  NORMAL  COLOR-PERCEPTION 
AMONG  THE  PERSONNEL  OF  THE  IMPERIAL  SWEDISH 
MARINE    AND    ARMY    CORPS. 

1st,  Upon  his  majesty's  recommendation,  the  sect.  54  of 
the  laws  of  the  Naval  School  require  that  every  cadet  must, 
besides  other  qualifications,  possess  normal  power  of  vision, 
together  with  normal  color-sensation. 

[Remark.  —  This  is  already  so  far  carried  out,  that  every 
cadet,  on  entering,  is  tested  as  to  his  color-perception. — F. 
Holmgren,  January,  1879.] 

2d,  In  the  general  orders  to  the  pilot  directory  it  is  re~ 
quired,  "  That  all  in  the  pilot-service,  ordinary  and  extra 
officials,  shall,  as  soon  as  may  be  determined  by  the  pilot 
directory,  be  examined,  to  find  if  they  have  normal  color- 
perception.  Those  who  do  not  have  the  power  of  distin- 
guishing the  colors  are  to  be  noted  in  the  list  by  the  pilot 
directory.  After  the  examination  the  number  of  color-blind 
in  each  district  is  to  be  recorded,  and  sent  in  to  the  chief  ot 
the  marine  department,  accompanied  by  such  suggestions 
for  action  as  may  be  considered  necessary." 

Given  at  the  Palace,  Stockholm,  Nov.  18,  1876,  by  im- 
perial order.  Freiher  F.  W.  von  Otter, 

Marine  Minister. 


256  COLOR-BLINDNESS  : 

[Remark.  —  These  examinations  have  been  already  car- 
ried out,  and  the  results  sent  in  to  me.  —  F.  Holmgren, 
January,  1879.] 

3d,  The  Regulations  of  the  Imperial  School  of  Navigation  of 
June  1,  1877,  Sect.  16,  2. 

Every  applicant  to  enter  the  navigation  department  of  the 
school  must  bring  a  physician's  certificate  as  to  the  condition 
of  his  color-perception.  A  fault  in  color-perception  will  not 
prevent  the  reception  of  the  candidate. 

[Remark.  —  This  last  must  be  soon  stricken  out,  or  al- 
tered. —  F.  Holmgren.] 

4th,  Royal  Orders  to  the  Chief  of  the  Military  Personnel  of 
the  Imperial  Marine. 

1st,  That  all  the  personnel  of  the  seamen's  and  boys' 
training-ship  shall,  at  the  next  general  review,  pass  the  sur 
geon's  examination  as  to  their  power  of  color-perception. 
Those  who  fail  shall  be  duly  recorded  on  the  crew's  manifest, 
and  a  notice  of  the  number  of  color-blind  in  each  company 
be  reported  by  the  mustering-officer  to  the  chief  of  the  ma- 
rine department. 

2d,  That  all  the  men  of  the  Imperial  Marine  Corps,  and 
boys  of  the  navy,  who  have  not  been  examined  in  accordance 
with  the  1st  regulation,  shall  be  tested  under  sect.  284  of 
the  Regulations  of  the  Marine,  3d  j)art,  of  the  required  medi- 
cal supervision.  The  company  report,  when  the  examina- 
tion was  before  the  man  went  on  board,  and  the  commander, 
when  this  test  was  after  he  was  on  board,  shall  take  note  of 
the  same,  to  be  reported  in  the  former  case  to  the  proper  mili- 
tary head,  who  will  report  to  the  chief  of  the  marine  depart- 
ment; in  the  latter  case,  the  commander,  who  will  follow  the 
rules  under  Rule  I.,  here  given. 

3d,  The  special  directions  in  reference  to  the  medical  ex- 
amination, in  accepting  the  recruit,  will  be  given  hereafter. 

Given  at  the  Palace  at  Stockholm,  Nov.  18,  1876. 

Freiher  F.  W.  von  Otter. 
II.  P.  Lilliehoek. 

[Remark.  —  The  examinations  ordered  in  1  and  2  are  long 
ago  carried  out,  and  the  results  handed  in  to  me.  In  refer- 
ence to  No.  3,  a  committee  of  military  surgeons  has,  in 
connection  with  the  other  regulations  of  acceptance  and  con- 


ITS   DANGERS   AND   ITS    DETECTION.  2o  i 

tinuance,  for  both  the  army  and  navy,  formulated  the  rules 
to  be  followed  under  No.  3.  This  has  been  since  published, 
and  is  now  only  awaiting  royal  sanction.  It  is  as  follows.  — 
F.  HoLMGREX,  January,  1879.] 

5th.  —  1st  Part,  Sect.  7. 

The  naval  service  calls  for  no  especial  bodily  condition 
other  than  the  physical  condition  required  in  the  line,  ex- 
cept the  addition  of  assured  normal  color-perception.  (  Vide 
the  Addendum.) 

Addendum.  —  Special  Examination,  Sect.  19. 

In  reference  to  normal  color-sense,  care  is  to  be  taken 
that  no  one  is  admitted  into  the  naval  service  whom  the 
examination  proves  to  be  in  any  degree  red-blind,  green- 
blind,  or  partially  color-blind. 

The  test  for  color-perception  is  to  be  carried  out  by  Pro- 
fessor Holmgren's  method,  by  which  partial  color-blindness 
is  determined  from  the  confusion  of  the  light  green,  or  first 
sample,  with  gray,  brownish  gray,  yellowish  green,  pale  red, 
or  pale  grayish  purple  (1,  2,  3,  4,  or  5). 

Red-blindness  is  determined  by  confusing,  with  the  pur- 
ple (II.),  blue  and  violet  (6  and  7)  ;  green-blindness,  by 
confusing,  with  the  purple,  green  and  gray  (8  and  9).  Com- 
pare "  Color-Bliudness  in  its  Relations  to  Railroads  and  the 
Marine,"  by  Frithiof  Holmgren. 

Sect.  21.  For  these  examinations,  the  following  appa- 
ratus, &c.,  is  necessary,  enclosed  in  a  box ;  viz.,  a  copy  of 
the  above-mentioned  book,  and  a  collection  of  the  worsteds. 

The  following  are  in  general  the  regulations  of 
the  Norwegian  Government  of  elate  May  7, 1877 :  — 

1st,  By  order  of  the  civil  department,  all  rail- 
road employes  are  examined  by  Professor  Holm- 
gren's method. 

2d,  By  order  of  the  navy  department,  the  pnpils 
in  the  navy-officers'  school  are  to  be  tested  for  color- 
blindness, as  also  all  enrolled  in  permanent  service. 

3d,  It  is  now  under  advisement  to  require  pilots 
to  be  tested  for  color-blindness ;  but  regulations 
are  not  yet  arranged  and  carried  out. 


258  COLOR-BLINDNESS  : 

Several  private  Swedish  steamsliip  companies 
have  ordered  examinations  of  their  crews. 

Through  the  efforts  of  Dr.  Favre,  the  personnel 
of  the  French  Transatlantic  Steamship  Company 
are  subjected  to  a  test  for  color-blindness.  The 
British  Cunard  Steamship  Company  requires  the 
surgeons  of  the  ships  to  test  the  men  for  color- 
blindness. Colored  glass  is  provided ;  but  the 
special  method  is  left  to  the  individual  medical 
officer.  If,  as  has  been  lately  stated  in  print,  the 
men  are  subjected  only  to  this  test  with  colored 
glass  or  colored  lanterns,  we  must,  from  all  that 
has  been  shown  and  proved,  consider  that  there 
has  been  no  test  as  to  the  true  color-sense  of  the 
personnel.  Asking  the  names  of  colors  or  of  col- 
ored lights,  &c.,  will  not  tell  us  just  how  the  per- 
son examined  sees  these  lights,  &c.  Steamship 
companies,  therefore,  when  they  think  they  have 
done  all  necessary  to  protect  the  lives  and  prop- 
erty intrusted  to  them,  may  thus,  from  want  of  a 
perfect  method  of  testing,  be  simply  gathering  into 
their  crews  men  whose  chromatic  defect  is  most 
dangerous,  and  who  could  not  obtain  employment 
when  a  perfect  test  was  applied. 

The  instructions  as  to  the  examination  of  per- 
sons seeking  employment  in  the  Bavarian  railroad 
service  are,  — 

I.  As  to  the  physical  capacity  of  each  individual, 
their  visual  power  is  to  be  tested,  and  also  theii 
color-perception ;  the  result  to  be  recorded  in  the 
report. 

IT.  The  test  for  color-blindness  is  to  be  con- 
ducted with  the  accompanying  worsteds,  which 
the  applicant  is  to  sort  by  colors,  and  designate. 


ITS   DAXGEES  AND   ITS   DETECTIOX.  259 

Only  those  who  can  distinguish  the  differences  of 
color  are  to  be  recorded  as  free  from  coior-hlind- 
ness.  All  other  cases  are  to  be  noted  with  the 
remark,  for  example,  —  "  Distinguishes  red  (or 
green)  with  difficulty." 

The  sanitary  inspector-general  of  the  railways 
of  Northern  Italy  replies,  — 

"  In  answer  to  your  question  on  color-blindness,  my  reply 
is,  that  although  no  printed  regulation  formed  by  the 
administration  for  our  railways  exists,  which  excludes  color- 
blind men  from  being  taken  into  the  service,  that  contin- 
gency is  guarded  against  by  instructions  given  to  the  sani- 
*^^ary  inspectors  of  the  company,  commissioned  to  examine 
the  candidates  for  employment  on  the  railways,  which  are 
to  this  effect :  that,  as  to  the  visual  faculty,  they  be  able 
clearly  to  distinguish  the  different  colors,  both  by  natural 
and  the  artificial  light  of  the  lamp  used  on  the  trains  and  in 
signal-boxes,  at  the  maximum  distance  of  normal  eyesight. 
These  instructions  have  been,  since  the  last  few  years,  very 
strictly  adhered  to  in  the  employment  of  new  engine-drivers, 
stokers,  and  signal-men,  —  in  fact,  of  all  who  have  part  of  the 
great  responsibility  of  the  safety  of  the  trains.  Owing  to 
this,  and  to  the  fact,  that,  when  the  least  doubt  arises  as 
to  the  perfect  state  of  the  eyesight  of  one  of  our  employes 
(due  to  age  or  sickness),  he  is  at  once  subjected  to  a  medi- 
cal examination,  wo  have  as  yet  had  to  lament  no  accident 
on  any  of  the  lines  under  our  direction  which  could  in  any 
way  be  attributed  to  color-blindness." 

The  minister  of  public  works  of  Belgium  pro- 
posed the  following  questions  to  the  Royal  Acad- 
emy:— 

1st,  Is  color-blindness  a  congenital  defect  ?  and 
can  it  be  acquired  ?  In  the  latter  case  the  admin- 
istration would  'periodically  test  its  agents. 

2d,  What  is  a  practical  and  efficient  method  of 
determinmg  whether  an  employe  fails  in  chromatic 
sense  ? 


260  COLOE-BLINDNESS  : 

The  committee  of  the  academy  replies,  — 

"  They  are  convinced  that  color-blindness  may  arise  from 
a  severe  disease,  contusions  or  wounds  of  the  head,  the  abuse 
of  tobacco  and  of  alcohol.  A  periodic  examination  of  the 
active  personnel  is  therefore  advised.  .  .  .  The  examina- 
tion of  those  suspected  of  color-blindness  should  consist  in 
making  them  sort,  according  to  their  colors,  worsteds  or  silks, 
chosen  especially  for  this  purpose.  The  color-blind  hesitate 
in  such  a  choice  as  this,  and  arrange  most  unexpected 
matches.  It  is  the  method  carried  out  by  Professor  Holm- 
gren. ...  A  change  or  modification  of  the  signal-colors 
used  has  been  proposed;  but  Professor  Holmgren  has  well 
answered  how  impracticable  this  would  be." 

I  have  noticed  elsewhere  (p.  134)  the  suggestions 
of  this  committee  as  to  attaching  colored  glasses, 
&c.,  to  the  engines,  to  assist  color-blind  engineers 
or  stokers. 

Dr.  Favre  states  that  the  examination  for  color- 
perception  has  been  in  force  on  the  Lyons  railroad 
since  1858.  In  March,  1870,  the  following  special 
questions  were  put  to  the  surgeons  of  this  road :  — 

1st,  How  many  candidates  have  you  examined  ? 
and  in  how  many  years  ? 

2d,  Since  when  have  you  tested  in  reference  to 
colors  ? 

3d,  How  many  color-blind  have  you  found  ? 

4th,  What  form  of  color-blindness  have  you 
found  most  frequent  ? 

5th,  Have  you  observed  color-blindness  from  ac- 
cident or  injury  ?  How  often  ?  How  long  did  it 
last  ?     What  were  the  circumstances  of  the  case  ? 

6th,  Have  you  written  on  the  subject  of  color- 
blindness, congenital  or  traumatic  ? 

The  reports  and  statistics  thus  gathered  I  have 
elsewhere  included.      In  1876  Dr.  Favre  reports 


ITS   DA^^GEES   AND   ITS   DETECTION.  261 

the  Dombes  et  Sucl-Est  and  the  Midi  roads  as  car- 
rying out  this  test. 

In  1 877  the  director-general  of  the  Holland  rail- 
roads called  npon  Professor  Bonders  of  Utrecht 
to  carry  out  the  examination  of  the  employes  for 
color-blindness.  This  was  done,  and  the  results 
I  have  already  given.  Professor  Bonders  drew 
up  the  instructions  for  the  guidance  of  the  twelve 
surgeons  deputed  to  carry  out  the  details  of  the 
first  examination,  and  a  final  official  report  was 
sent  in  to  the  director-general. 

I  have  received  from  Professor  Bonders  the 
printed  blank  required  hereafter  to  be  filled  out 
in  the  case  of  every  railroad  employe.  Every 
candidate  for  service  must  pass  an  examination 
by  one  of  five  ophthalmic  surgeons  in  Amsterdam, 
Rotterdam,  Anheim,  Utrecht,  and  Leyden.  These 
surgeons'  names  and  hours  for  examinations  are 
printed  on  the  back  of  the  blank,  the  face  of 
which  reads  as  follows  :  — 

Netherlands  Railroad  Company.  —  The  undersigned 
states  that  the  sight  of is  sufficient  (a)  for  the  employ- 
ment of  engineer  or  fireman ;  (&)  for  the  employment  of 
station-master  or  those  who  may  fill  his  place,  assistants, 
haltmaster,  director,  first  conductor,  conductor,  porter,  brake- 
man,  switchman,  ranker,  bridgekeeper,  linekeeper,  or  line- 
keeperess. 

The  Ophthalmic  Surgeon. 

The  187  . 

(Signature  of  the  examined  to  be  given  in  the  presence 
of  the  surgeon.) 

N.B. — In  case  the  candidate  desires  employment  under 
a,  &  is  to  be  stricken  out,  and  the  reverse. 

There  is  required,  for  a,  eyes  and  eyelids  healthy  exter- 
nally, without  habitual  congestion  or  inflammation  ;  field  of 
vision,  not  limited  in  either  eye;  acuteness  of  vision,  nor- 


262  COLOR-BLINDNESS  : 

mal;  refraction, normal;  color-perception,  at  least  four-fifths 
according  to  Donders's  method.  For  h,  eyes  and  eyelids  ex- 
ternally healthy,  without  habitual  congestion  or  inflamma- 
tion ;  field  of  vision,  not  limited  in  either  eye ;  normal 
acuteness  of  vision  in  one  eye ;  normal  refraction ;  color- 
perception,  at  least  three-fifths ;  with  the  other  eye,  acute- 
ness of  vision  at  least  one-half ;  color-perception,  one-half. 

These  •examinations  are  required  by  the  royal 
official  regulations  of  Jan.  31,  1879,  published  in 
the  "  Nederlandische  Staats-Courant "  of  March 
3,  1879,  chap.  v.  art.  85 :  — 

"  All  employes  must  be  able  to  read  and  write  and  pos- 
sess normal  power  of  vision,  so  far  as  this  is  required  for 
the  proper  performance  of  their  duty. 

"  Employes  who,  by  the  decision  of  the  minister  of  the 
department  of  industry,  commerce,  and  the  navy,  are  con- 
sidered unfit  to  perform  their  duty,  are,  at  the  request  of 
the  minister,  to  be  discharged  by  the  managers  of  the  rail- 
roads." 

Regulations  were  also  proposed  to  the  govern- 
ment by  Professor  Donders  in  reference  to  the 
navy  and  merchant  marine  ;  and  they  are  now 
accepted  and  enforced,  as  seen  from  an  order  in 
the  same  official  paper :  — 

"  The  minister  of  the  department  of  industry,  commerce, 
and  the  navy,  referring  to  art.  2  of  the  royal  decree  of  Feb. 
17,  1879  (Staatsblad,  No.  37),  in  regard  to  the  carrying 
out  directions  for  the  examination  for  a  warrant  as  mate  in 
the  merchant  marine,  as  directed  by  royal  order  of  May  5, 
1877  (Staatsblad,  No.  98),  has  decided  to  require, — 

"  1st,  In  the  test  for  visual  acuteness  and  color-sensation 
ordered  in  the  article,  the  following:  — 

"a  —  Normal  vision  without  correcting  glasses  with  one 
eye,  and  at  least  one-half  of  normal  vision  with  the  other 
eye. 

"6  —  Both  eyes  m  ist  be  without  manifest  hypermetropia 
of  a  degree  above  D^'  .00,  and  in  one  eye  at  least  nominal 
vision. 


ITS   DANGERS    AXD   ITS   DETECTION.  263 

''  c —  Visual  field  not  limited  in  either  eye. 

'vZ  —  Eyes  and  eyelids  externally  healthy,  Tvithout  habit- 
ual congestion  or  irritation. 

"e  —  Color-perception  perfect  for  transmitted  light  in  one 
eye,  and  at  least  one-half  in  the  other  ;  according  to  Don- 
ders's  method. 

"  2d.  The  report  and  declaration  of  the  expert,  as  re- 
quired in  the  above,  shall  be  considered  valid  for  one  month 
only  from  the  time  the  test  is  made. 

'■TaK   VAX    POOETVLIET. 

"  Geatesthage,  Feb.  27, 1879." 

By  the  same  order  three  ophthalmic  surgeons 
are  appointed  as  the  experts  for  these  examina- 
tions in  Amsterdam,  Rotterdam,  and  Leeuwarden. 

In  England,  Parliament  has  never  enacted  any 
laws  in  reference  to  the  control  of  color-blindness 
among  railway  employes  or  the  navy  and  mercan- 
tile marine,  so  far  as  I  can  at  present  ascertain. 
The  individual  railroad  corporations  have,  how- 
ever, taken  steps  in  this  direction  in  regard  to 
their  men.  Professor  Wilson  says,  in  1856,  "  I  am 
happy  to  say  that  the  publication  of  my  papers 
has  induced  the  Great  Northern  Railway  Company 
to  requu^e  that  in  future  all  their  porters  shall  be 
tested  as  to  their  freedom  from  color-blindness 
before  they  are  admitted." 

A  terrible  accident  at  Arlsey,  Dec.  23,  1876, 
called  out  replies  from  railroad-surgeons  to  news- 
paper articles  in  reference  to  this  point  of  control. 
In  ''  The  London  Times  "  of  Jan.  1, 1877,  Mr.  S.  L. 
Mason  v/rites,  — 

"The  risks  incident  to  the  peculiar  physical  defect 
known  as  color-blindness,  railway  managers  have  long  been 
alive  to.  On  our  leading  lines,  without  exception,  precau- 
tions are  taken  against  the  employn  at  of  men  subject  to 
that  disqualification.     In  Mr.  Seymour  Clark's  time,  when 


264  COLOR-BLINDNESS  : 

I  was  connected  with  the  Great  Northern  Railway,  this 
matter  was  scrupulonsly  attended  to,  and,  no  doubt,  is  so  still 
under  the  present  able  management.  At  the  date  I  speak 
of  —  ten  years  ago  —  no  porter,  even  though  destined  to 
work  in  a  goods-shed,  would  be  certified  as  eligible  for  ap- 
pointment by  the  board  until  his  eyesight  should  have  been 
subjected  to  certain  prescribed  tests,  among  which  was  the 
discrimination  of  colors,  especially  those  used  in  railway- 
signals." 

Other  testimony  was  given  in  "  The  Times," 
"  The  Lancet,"  &c.,  that  railroad  employes  were 
tested  on  several  different  lines  by  Mr.  Oliver 
Pemberton  of  Birmingham,  Mr.  C.  Puzey  of  Liv- 
erpool, Mr.  Page  of  Carlisle,  and  Dr.  Jaspar  Mc- 
Aldin.  Li  the  medical  discussions,  however,  it 
was  shown  that  the  tests  applied  to  detect  color- 
blindness were  Yeij  faulty  and  wholly  inadequate. 
In  consequence  of  the  use  of  methods  requiring 
only  the  color-name  of  objects  or  railroad-signals, 
the  surgeons  were  deceived  into  the  idea  that  color- 
blindness was  not  as  frequent  as  Professor  Wilson 
had  shown  it  to  be.  The  public  fears  excited  at 
the  time  of  the  Arlsey  accident  were  thereby  un- 
fortunately quieted.  No  better  proof  is  needed  of 
the  necessity  of  a  uniform  and  certain  test  being 
applied  to  employes  than  the  facts  and  discussions 
of  the  Arlsey  accident. 

Dr.  D.  Argyll  Robertson  of  Edinburgh  kindly 
writes  me  of  date  March  9,  1879,  — 

"  I  trust  that  the  following  facts,  which  I  have  ascertained 
through  the  surgeons  to  the  North-British  (Dr.  Dunsmure) 
and  the  Caledonian  (Dr.  John  Duncan)  Railway  Companies, 
may  be  of  service  to  you.  I  may  mention  that  these  are  the 
two  chief  railway  companies  in  Scotland ;  the  North-British 
possessing  930  miles  of  railway,  and  the  Caledonian  753 
miles. 


ITS   DAXGEES   AXD   ITS   DETECTIO^T.  265 

"  North-British  Railway.  —  Since  about  1865  or  1866, 
when  Dr.  Dunsmure  directed  the  attention  of  the  manager  of 
the  company  to  the  subject,  both  engine-drivers  and  stokers 
are  invariably  examined  as  to  color-perception  before  being 
engaged.  The  men  are  tested  by  means  of  a  board  uith 
ten  different  colors  upon  it.  Three  men  have  been  rejected 
on  account  of  color-blindness  since  examinations  were  in- 
stituted. 

"  Caledoniax  Railway  Company.  —  Before  any  one 
is  employed  as  signal-man  or  guard,  he  is  first  examined  by 
a  doctor,  and  especially  as  to  his  sight,  and  power  of  dis- 
tinguishing colors.  Only  about  one  in  a  year  is  rejected  on 
account  of  color-blindness. 

"All  engine-drivers  are  tested  as  regards  perception  of 
color  when  they  are  j>assed  from  'firing'  to  'driving,'  and 
no  case  of  color-blindness  has  yet  been  met  with.  This, 
however,  is  probably  due  to  the  circumstance  that  the  men 
are  aware  that  they  are  to  be  tested,  and  do  not  persevere 
as  stokers  if  they  considered  they  were  not  competent  to 
pass  as  drivers.  .  .  .  There  is  no  legislation  here  enforcing 
such  examinations." 

Abundant  proof  has  been  given  in  this  volume 
of  the  inadequacy  of  such  tests  as  are  thus  shown 
to  be  at  present  used  on  these  Scotch  roads,  as 
well  as  on  the  various  English  roads,  from  the 
evidence  of  the  surgeons  connected  with  them. 
No  wonder  so  few  color-blind  are  detected.  A 
simple  act  of  Parliament  enforcing  universally 
such  a  test  as  Holmgren's  or  Donders's  would 
insure  safety,  as  the  medical  officers  of  the  roads 
are  perfectly  competent  to  properly  carry  out  such 
examinations. 

"  Order  of  the  Handelministerium  of  Prussia,  March,  1877, 
published  in  the  Official  Paper  of  the  Government  of  the 
Interior,  1877. 

"In  consequence  of  the  frequent  occurrence  of  cases  of 
so-called  color-blindness,  and  the  great  dangers  which  may 
arise  from  the  same  on  the  railroads,  it  is  recommended,  — 


2G6  COLOE-BLINDNESS  : 

"  1st,  That  persons  in  the  outside  railroad  service,  sucl* 
as  station  officials,  i3ointsmen,  signal-men,  engineers,  stokers, 
brakemen,  and  conductors,  be  first  tested  as  to  their  color- 
perception  before  being  employed. 

"  2d,  That  all  those  not  engaged  in  the  above-mentioned 
positions  be  tested  for  color-blindness,  in  order  to  eliminate 
the  red  or  green  blind  from  positions  where  the  recognition 
of  the  colored  signals  is  requisite. 

"3d,  This  examination  is  also  to  be  made  of  convales- 
cents where  it  is  requisite ;  namely,  after  typhus-fever,  in- 
juries of  the  head,  severe  contusions,  and  the  like,  as  also 
in  general  to  be  repeated  every  five  years. 

"  If  this  examination  is  to  be  carried  out  over  a  large 
district  by  a  recogilized  ophthalmic  surgeon,  it  would  neces- 
sitate numerous  journeys  of  the  officials  and  employes,  and 
cost  much  time.  It  is  suggested  that  it  is  within  the  pro- 
posal of  the  imperial  direction  to  consider  that  any  physi- 
cian, even  if  he  has  not  made  a  specialty  of  diseases  of  the 
eye,  can  carry  out  this  test  with  sufficient  exactness  to  insure 
safety :  therefore  the  imperial  railroad  directory  is  advised 
to  have  the  proposed  examination  conducted  by  the  several 
district  railroad-surgeons." 

In  accordance  with  the  order  of  the  Handel- 
ministerium  of  Sept.  19,  1877, — 

"  The  examination  is  to  decide  whether  the  person  tested 
can  correctly  distinguish  red,  green,  and  violet  by  daylight, 
and  also  by  artificial  light,  or  whether  there  is  the  slightest 
suspicion  of  color-blindness :  therefore  the  examination 
must  be  done  by  an  ophthalmic  surgeon." 

In  reference  to  the  regulations  and  mstructions 
for  these  examinations,  I  will  quote  from  Dr. 
Magnus  of  Breslau,  as  what  he  states  is  pertinent 
to  all  such  tests,  and  therefore  extremely  important 
for  us  here  in  the  United  States,  where  the  whole 
subject  is  new.     He  says,  — 

"  The  very  great  necessity  of  good  color-perception  on  the 
part  of  railroad  employes,  concerning  as  it  does  the  safety 
of  the  public  roads,  has  already  excited  general  attention, 


ITS   DANGERS   AXD   ITS   DETECTIOX.         267 

thanks  to  the  imtirin,^  efforts  of  Professor  Holmgren.  And 
it  has  led  already  to  valuable  practical  measures ;  but  yet  it 
has  seemed  to  us,  that,  precisely  on  this  point,  certain  re- 
forms are  very  desirable.  The  regulations  from  the  au- 
thorities for  the  purpose  of  avoiding  the  possible  results  of 
the  action  of  color-blind  oflBcials  are,  and  rightly  so,  first 
directed  towards  a  most  careful  test  of  the  color-sense  of 
all  the  employes.  All  candidates  are  to  be  examined,  and 
all  those  in  service  equally  thoroughly  tried  for  color- 
blindness. A  similar  examination  of  the  whole  personnel 
is  to  be  carried  out  every  five  years.  A  general  examina- 
tion for  color-blindness  is  directed  by  the  regulations  of  the 
authorities.  The  method  and  the  way  and  means  of  con- 
ducting this  examination  are,  however,  undetermined.  The 
choice  of  methods  is  rather  left  to  the  fancy  of  the  examin- 
ing surgeon  ;  or,  if  a  method  is  advised  him,  this  is  not 
always  the  same,  the  several  railroad  managers  varying 
greatly  in  this  respect.  But  the  result  of  every  test  for 
color-perception  is  very  dependent  upon  the  method  em- 
ploj'ed.  Now,  the  various  methods  at  present  used  are  not 
of  the  same  value.  Some  of  them,  on  the  contrary,  give 
very  unreliable  results ;  whilst  others  leave  but  little  to  be 
desired  in  respect  to  precision.  Hence  the  values  of  the 
reports  of  the  several  examinations  on  the  various  German 
roads  are  not  the  same,  but  exhibit  great  and  doubtful 
variations.  If  we  could  compare  the  percentage  from  the 
statistics  of  all  the  German  roads  of  the  extent  of  color- 
blindness, we  should  see  within  what  limits  such  percentage 
varies,  and  how  the  results  of  the  individual  examiners 
differ.  For  example,  "  The  Breslau  Journal  "  of  Oct.  10, 
1878,  reports  the  test  of  1,348  employes  of  one  of  the  roads 
here,  and  the  finding  of  but  10  color-blind  (or  0.74  per 
cent)  ;  whilst  one  of  my  colleagues,  who  tested  the  employes 
of  another  road,  told  me  he  found  4  per  cent. 

"  We  see,  therefore,  that  the  test  for  color-blindness,  as  it 
is  now  carried  out  on  our  German  roads,  does  not  fulfil  the 
object  desired.  Absolute  safety  of  the  traffic,  with  due  regard 
to  the  interests  of  the  personnel,  cannot  be  gained  by  such 
differing  and  uncertain  data.  To  obtain  the  great  benefit  of 
an  obligatory  examination  of  the  color-sense  of  the  railroad 
employe's,  the  varying  reports  as  to  the  extent  of  color-blind- 


2G8  COLOR-BLINDXESG  : 

ness  must  be  corrected,  and  greater  unity  obtained  This 
can  only  be  done  by  one  and  the  same  method  being  required 
on  all  our  roads.  Hence  it  will  be  asked,  which  of  the  present 
methods  is  most  practical,  and  has  so  stood  the  test  of  em- 
ployment as  to  be  naturally  called  for  in  the  interest  of 
the  safety  of  the  public  communications'?  The  answer  to 
this  very  important  question  will  be  governed  by  a  critical 
analysis  of  the  several  methods  of  testing.  In  my  examina- 
tion of  5,486  persons  I  have  very  particularly  considered  this 
very  point,  and,  from  my  experience,  decided  that  the  method 
of  Professor  Holmgren  of  Upsala  is  the  one  giving  us  the 
most  exact  results  in  testing  large  numbers.  It  is  so  su- 
perior to  the  other  present  methods,  in  exactness  of  result 
and  convenience  of  use,  as  to  render  it  undoubtedly  the 
best.  In  such  an  important  question  the  opinion  of  a  single 
observer  should  not,  of  course,  be  taken  alone,  but  others' 
e'xperience  also  heard  and  considered.  In  doing  this  we 
shall  find  similar  favorable  opinions  of  Holmgren's  method 
from  those  who  have  used  it.  Thus  Dr.  Colin,  in  Breslau, 
in  his  criticism  of  the  several  methods  of  testing,  declares 
Holmgren's  to  be  the  best.  We  hear  the  same  from  Professor 
Pfliiger  in  Berne,  and  from  Dr.  Jeffries  in  Boston.  The  latter 
is  so  convinced  of  the  superiority  of  Holmgren's  method, 
that  he  writes  me  of  date  Sept.  19,  1878,  from  Boston,  as 
follows  :  '  My  own  experience  teaches  me  the  great  value  of 
Holmgren's  method  over  all  others,  and  I  wish  it  would  be 
ordered  by  your  Kaiser  throughout  Deutschland.' 

"  In  interest,  therefore,  of  the  safety  of  railroad  travel,  we 
feel  called  upon  to  require  the  following  :  That  the  test  for 
color-blindness  now  obligatory  on  most  of  the  German  roads 
should  be  the  same  and  identical  throughout  the  empire, 
and  carried  out  in  the  same  way  on  every  railroad ;  and  that 
Holmgren's  method,  being  the  most  certain  and  most  prefer- 
abl,  should  be  alone  employed  for  this  purpose." 

The  value  and  truth  of  this  quite  moderate 
criticism  of  Dr.  Magnus  can  best  be  proved  by 
showing  what  has  been  done  on  a  number  of  the 
German  roads.  This  I  am  enabled  to  do  from  a 
lecture  given  by  Dr.  E.  Gintl,  Central  Inspector 


ITS   DANGEES   AND   ITS   DETECTION.  2G9 

of  the  Lemberg-Czernowitz-Jassy  road  at  Vienna, 
April  2,  1878,  before  the  society  of  Austrian  rail- 
road officials.  After  an  introductory  sketch  of 
color-perception,  &c.,  and  some  of  the  methods 
of  testing  for  color-blindness,  he  says,  "It  will 
thus  be  seen,  that,  for  the  examination  of  the  em- 
ployes in  general,  any  of  the  methods  may  be  used. 
Stilling's  or  Holmgren's  tables,  or  the  colored 
charts,  or  Waldstein's  apparatus,  are  quite  suffi- 
cient ;  but,  to  decide  the  doubtful  cases  or  the  indi- 
vidual colors,  only  the  spectroscopic  apparatus  of 
Schmidt  and  Hausch  in  Berlin  can  be  employed 
with  certainty,  as  I  have  personally  proved  in  the 
testing  of  a  very  large  number  of  persons."  He 
gathered  the  reports  from  forty-six  railroads,  on 
which  41,444  employes  were  tested,  and  319  color- 
blind found,  —  a  percentage  of  0.769.  I  here  give 
these  reports :  — 


270 


COLOR-BLINDNESS  : 


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ITS  DANGERS  AKD   ITS   DETECTION. 


271 


All  red-greon-blind. 
Tests  not  finished. 
Tests  not  finished. 

3  red-green ;  10  blue-green ;  1  ycl- 
low-green. 

29  red-green;  1  blue-orange;  1 
violet-yellow;  5  blue-green;  1 
blue-yellow;  8  could  not  dis- 
tinguish. 

Tests  not  finished. 

Red-green-bUnd. 
No  report  made. 

4  red-green ;  1  uncertain  in  blue ; 
1  red-blue;   1  uncertain  in  yel- 
low ;  1  without  color-sense. 

No  ofilclal  examination. 

1  red-green  and  red-blue,  2  red- 
green  blind. 

Blue-red  and  yellow-green  blind. 

All  red-green-blind. 

Tests  not  finished. 

From  January,  1877,  new  employes 
to  bo  tested;  old  ones  not. 

Colored     tables     and 

glasses 
Stilling's,  Vierordt's  . 

Colored-paper  tables  . 

Stilling's    tables    and 
colored  papers 

Green  and  red  glasses, 
and  targets 

and  targets 

Stilling,'  Viel-ordt        '. 

Stilling's  tables    . 
Stilling's  tables    . 

Stilling's  tables   !       '. 

0.46 

i.76 
0.75 

6.11 
6.55 

6.26 

1.47 
0.97 

d 

<0                  •>*       ift                            r-l            00                       CO       iHt- 

i 

1,308 

800 
6,287 

880 
1,457 

1,500 

68 
719 

1 

July,  1877, 

Dec,  1877, 
Dec,  1877, 
Aug.,  1877, 

Juna,  1877, 

Mar.  ,'1878, 
July,' 1877, 

June,' 1877, 

Oct.,  1877, 
July,  1877, 

Jan.,' 1877, 

Nassau  u.  Taunus  Bahn, 

Niedermiirkische  Bahn . 
Obsscldesiseho  Bahn      . 
Oldenburgischo      . 

Ost-bahn,  preusa    . 

rfiilzische  Eisenbahn     . 
Eechte  Oder  Uferbahn  . 

Rheinische  Eisenbahn   . 
Saarbrucken  Eisenbahn, 

SUchs.  Staatsbahn  . 
Thiiringische  Eisenbahn, 

Weimar-Gera  Eisenbahn, 
Wcrra  bliseubahn  . 
Wcwtphalische  l<:isenb.  . 
Wiirttemburg  Staatsb.   . 

1 

S    S^S    S             §5^    ^S          ^S    SliSa 

272 


COLOE-BLINDNESS 


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ITS  DANGEES   A^D   ITS   DETECTION. 


273 


i^§ 


274  COLOR-BLINDNESS  : 

Contrasting  these  results  with  those  where  a 
a  thorough  test  gave  us  as  in  France  5.77,  in 
Switzerland  6.28,  in  Sweden  2.15,  and  in  Fin- 
land 14.01,  and  we  can  readily  appreciate  the 
force  of  Dr.  Magnus's  criticism,  and  my  remark 
above,  that  but  here  and  there  can  the  color-blind 
employes  have  been  detected  on  the  German 
roads. 

I  have  also  given  this  long  list  of  railroad  ex- 
aminations, collected  by  Dr.  Gintl,  as  a  warning 
to  our  railroad  corporations  in  this  country,  and 
to  the  examiners  they  shall  hereafter  employ. 
The  several  German  railroads'  surgeons,  not  being 
officially  directed  to  employ  Holmgren's  method, 
and  unfortunately  hearing  it  spoken  and  written 
about  in  a  tone  of  doubt,  naturally  chose  other 
methods  they  individually  knew  of.  Moreover, 
some  of  the  German  physicians  who  had  paid 
especial  attention  to  this  subject,  and  who  had 
tested  some  thousands  of  persons  for  color-blind- 
ness by  Holmgren's  method,  deliberately  misap- 
plied it,  in  absolute  contradiction  to  his  express 
and  very  explicit  directions.  Thus,  to  detect 
whether  a  person  is  color-blind,  we  have  seen  that 
a  peculiar  shade  of  green  worsted  is  used,  and  the 
examined  directed  to  pick  out  what  looks  like  it, 
lighter  or  darker.  A  purple  (German,  7'osa)  is 
used  to  decide  whether  a  person  is  red  or  green 
blind.  This  latter  is  not  to  be  used  to  detect 
color-blindness,  but  only  which  form  of  the  defect 
we  have.  Nevertheless  Dr.  Cohn  of  Breslau,  in 
reporting  his  results  to  the  Heidelberg  Ophthalmo- 
logical  Society,  1878,  says,  ''  As  the  very  best  and 
the    quickest   method   of   first   testing   for   color- 


ITS   DANGERS  AND   ITS   DETECTION.  275 

blindness,  I  must  again  and  again  recommend  the 
purple  worsted.  It  has  served  perfectly."  He  also 
speaks  of  the  colored  plate  attached  to  Holm- 
gren's book,  and  copied  in  this  volume,  as  being 
as  bad  to  detect  color-blindness  with  as  the  pur- 
ple worsted  is  good.  Now,  this  plate  is  only  in- 
tended, and  so  most  definitely  described,  to  illus- 
trate the  colors  to  be  used,  and  the  colors  of 
confusion  or  mistakes  of  the  defective.  This 
ignoring  Holmgren's  explicit  directions  as  to  the 
carrying  out  of  the  test  with  the  green  worsted, 
and  then  speaking  of  the  colored  plate  as  if  that 
had  been  proposed  to  be  used  by  Holmgren,  was 
most  unfortunate  and  misleading.  It  has  naturally 
led  others  to  follow  him  without  reading  Professor 
Holmgren's  book.  Dr.  Cohn  tried  Stilling's,  as 
also  other  methods,  but  found,  as  every  examiner 
will,  Holmgren's  the  most  convenient  and  prac- 
tical. 

Thus  the  reports  I  have  quoted  of  the  German 
roads  show  most  conclusively  that  from  a  faulty 
method  of  testing  only  here  and  there,  so  to 
speak,  have  the  color-blind  employes  been  de- 
tected. This  is  very  unfortunate,  as  it  throws,  for 
the  time  being,  a  certain  doubt  over  the  whole 
question  of  the  frequency  of  color-blindness,  its 
danger,  the  necessity  for  control,  and  the  elimina- 
tion of  the  defective.  Moreover,  the  entire  work 
in  Germany  will  have  to  be  done  over  again. 
Probably,  from  what  I  lately  learn,  the  correct 
tests  are  now  being  officially  ordered,  and  carried 
out.  Thanks  to  the  energy  of  Professor  Holm- 
gren in  Sweden,  the  affair  was  there  better  con- 
ducted.     The  government   first   ordered  the  use 


276  COLOE-BLINDNESS  : 

of  the  flags  and  lanterns  by  the  railroad  officials 
to  test  for  color-blindness ;  but,  when  Holmgren 
showed  them  the  uselessness  of  this,  they  ordered 
his  test,  and  also  required  all  the  railroad-sur- 
geons to  learn  it  of  him,  and  carry  it  out  properly. 

From  a  lecture  on  color-blindness  by  Dr.  A.  von 
Reuss  of  Vienna,  and  a  letter  of  date  March  17, 
1879,  I  am  able  to  still  further  substantiate  the 
criticisms  I  have  made  or  introduced  in  reference 
to  the  examinations  of  the  German  employes. 

The  Austrian  Handelministerium  ordered  Nov. 
18,  1876,  that  "  persons  who  could  not  distinguish 
the  signals  on  account  of  near-sightedness  or  color- 
blindness were  not  to  be  admitted  into  the  ser- 
vice." This  led  to  the  carrying-out  of  the  exami- 
nations as  above  given  with  such  unsatisfactory 
results.     Dr.  von  Reuss  says,  — 

"  Why  these  differ  so  greatly  from  the  numbers  reported 
by  ophthalmic  surgeons  was  readily  seen  from  the  original 
reports  sent  in  to  Dr.  Gintl,  and  which  he  kindly  allowed 
me  to  see,  from  which  reports  the  data  of  the  tables  were 
collected.  In  these  reports  are  mentioned  blue-red-blind, 
blue-black-blind,  green-blue-blind,  violet-black-blind,  yeL- 
low-red-blind,  &c.,  and  this  where  Stilling's  tables  had  not 
been  used,  which  might  have  given  rise  to  such  confusion. 
This  is  a  proof  that  the  examiners  did  not  know  what  they 
were  about.  The  majority  of  the  examinations  are  there- 
fore useless." 

In  this  lecture  Dr.  von  Reuss  reports  testing 
593  employes,  and  finding  3.2  per  cent  color-blind. 
In  his  letter  to  me  of  March  17,  1879,  he  says,  "  I 
have  tested  600  employes  of  the  Elizabeth- West- 
bahn,  and  found  3.5  per  cent  color-blind."  He 
employed  Professor  Donders's  method  with  the 
worsteds. 


ITS   DANGERS   AXD   ITS   DETECTION.  277 

The  unsatisfactory  results  of  the  examinations 
by  the  several  railroad-surgeons,  clue  to  a  want  of 
knowledge  and  the  lack  of  a  uniform  and  certain 
test,  led  to  the  following  order  from  the  Handel- 
ministerium :  — 

ORDER  OF  THE  HAXDELMIXISTERIUM,  OCT.  15,  1878,  TO 
ALL  THE  RAILROAD  CORPORATIONS,  RESPECTING  PRO- 
FESSOR  HOLMGREN'S  METHOD   OF    TESTING  COLOR-BLIND- 

XESS. 

My  frequent  attention  having  been  called  to  the  work  of 
Professor  Holmgren,  "  De  la  Cecite,''  &c.,  I  have  obtained 
professional  opinions  as  to  the  method  of  testing  color-blind- 
ness proposed  in  it,  showing  it  to  be  practical  and  very  sim- 
ple, and  perfectly  answering  the  requirements.  The  method 
consists  in  causing  the  examined  to  select  from  a  number  of 
skeins  of  colored  worsteds  all  those  corresponding  to  a  pat- 
tern shown  him.  The  examiner  decides  from  the  manner  in 
which  this  is  done.  A  normal-eyed  will  select  four  or  five 
skeins  in  a  minute,  and  the  color-blind  will  as  quickly  make 
such  characteristic  mistakes  as  to  render  the  immediate 
diagnosis  possible.  In  doubtful  cases,  and  where  deception 
is  supposed,  a  more  thorough  test  must  be  applied,  with,  for 
instance,  a  spectrum  apparatus. 

As  experience  has  shown  that  color-blindness,  besides 
being  congenital,  may  be  acquired,  safety  requires  that  not 
only  should  those  entering  service  be  tested  as  to  their  per- 
ception of  the  three  primary  colors, — red,  green,  and  violet, 
—  but  that  the  test  should  be  repeated  periodically,  and 
especially  after  diseases,  and  contusions  of  the  head. 

I  desire  to  call  the  attention  of  the  corporations  to  the 
book  above  mentioned,  and  would  ask  their  consideration  of 
the  suggestions  here  briefly  made,  since,  from  the  necessary 
apparatus,  the  examinations  of  employes  has  hitherto  been 
expensive  and  inconvenient ;  and  this  method  therein  pro- 
posed greatly  simplifies  and  facilitates  the  testing  for  color- 
blindness. 

K.-K.  Handelminister  Chlumetzky. 
ViEXXA,  Oct.  15,  1878. 

Jan.  8,  1879,  in  the  House  of  Representatives 


278  COLOR-BLINDNESS  : 

of  the  legislature  of  Massachusetts,  Mr.  Hamilton 
A.  Hill  of  Boston  introduced,  at  my  request,  the 
following  order :  — 

"  That  the  Committee  on  Railroads  inquire  whether  any 
and  (if  any)  what  legislation  is  necessary  in  reference  to  the 
employment  by  railroad  companies,  in  certain  responsible 
positions,  of  persons  affected  with  color-blindness." 

This  order  was  passed  by  the  House,  and  a  pub- 
lic hearing  given  as  follows  :  — 

COMMONWEALTH  OF  MASSACHUSETTS. 

Committee  on  Railroads. 

State  House,  Boston,  Jan.  13, 1879. 

The  Committee  on  Railroads  will  give  a  hearing  to  par- 
ties interested  in  an  order  relative  to  legislation  in  reference 
to  the  employment  by  railroad  corporations,  in  certain  re- 
sponsible positions,  of  persons  afflicted  with  color-blindness, 
at  room  No.  10,  State  House,  on  Wednesday,  Jan.  22,  at  ten 
o'clock  A.M. 

Edwin  W.  Marsh, 
Clerk  of  the  Committee. 

By  invitation  of  the  Committee  on  Railroads  I 
appeared  at  this  hearing,  and  argued  in  support  of 
the  conclusions  contained  in  this  volume.  My 
statements  were  supported  by  European  statistics, 
and  my  own  collected  in  this  community,  by  ex- 
periments in  reference  to  color-perception,  the 
exhibition  of  various  tests,  &c.,  and  by  the  practical 
illustration  of  the  value  of  Professor  Holmgren's 
method  in  detecting  the  chromatic  vision  of  sever- 
al color-blind  who  were  present  at  the  time. 
There  was  no  opposition  to  my  statements  or  con- 
clusions. 

As  the  result  of  this  hearing,  the  Joint  Commit- 
tee on  Railroads  reported,  Feb.  28,  1879,  in  the 
Senate,  the  following  resolve  :  — 


ITS   DANGEBS   AND   ITS   DETECTION.  279 

"  That  the  board  of  railroad  commissioners  be  instructed 
to  consider  ^ivhether  any  legislation  is  expedient  or  needful 
with  reference  to  the  employment  by  railroad  corporations 
of  persons  afflicted  with  color-blindness." 

This  was  passed  in  tlie  House  of  Representa- 
tives March  21,  1879,  and  in  the  Senate  March  24, 
1879;  receiving  the  signature  of  the  governor 
March  25,  1879. 

It  is  thus  seen  that  Massachusetts  has  been  the 
first  State  to  take  action  in  reference  to  the  con- 
trol of  color-blindness  on  the  railroads.  She  pos- 
sesses, of  course,  no  authority  on  the  water.  There 
the  General  Government  must  a6t  in  concert  with 
other  nations.  It  is  now  in  the  hands  of  the  Mas- 
sachusetts raiboad  commissioners  to  carry  for- 
ward the  work  of  investigation,  and  report  here- 
after to  the  legislature.  If  they  can  induce  the 
several  railroad  corporations  to  meet  the  just 
demands  of  the  community,  and  eliminate  the 
color-blind  from  their  employ,  then  a  law,  subse- 
quently enacted,  can  be  based  upon  the  result  of 
the  examinations,  and  made  to  meet  all  require- 
ments of  the  future.  This  law  of  control  should 
also,  as  in  Europe,  require  the  proof  by  test,  of 
normal  visual  power  for  form^  as  well  as  normal 
color-sense. 

It  is  to  be  hoped  that  the  other  States  will 
quickly  follow  the  action  of  Massachusetts.  The 
advantages  of  a  uniform  law  throughout  the 
country,  and  a  uniform  and  absolutely  certain 
system  of  testing  for  color-blindness,  I  need  not 
dwell  upon  here,  since  it  is  self-evident  from  what 
I  have  brought  forward  in  this  volume.  There 
will  be  no  excuse  for  such  blunders  as  were  made 


280  COLOE-BLINDNESS  : 

in  Europe,  now  that  we  liave  the  benefit  of  them 
m  this  country. 

I  have  spoken  of  my  action  and  its  results,  in 
order  that  my  professional  brethren  in  other  States 
may  see  how  my  efforts  were  successfully  carried 
out,  and  be  able  to  refer  to  them  when  themselves 
undertaking  similar  work  in  their  own  communi- 
ties. 


ITS  DANGERS   AND  ITS  DETECTION.  281 


CHAPTER  XXIV. 

PERSONAL  EXPERIENCE  WITH  HOLMGREN'S  METH- 
OD. —  SUGGESTIONS  AS  TO  ITS  USE. 

The  experience  which  I  have  gained  in  the  use 
of  Holmgren's  method  of  detecting  color-blindness 
by  the  worsteds  is,  I  think,  worth  here  recording 
for  the  benefit  of  my  brother  ophthalmic  surgeons, 
whom  the  railroads  may  hereafter  ask  to  test  the 
employes  of  their  roads.  First,  as  to  the  choice  of 
the  worsteds  themselves,  since  a  good  deal  depends 
on  this:  Proper  colors  can  be  obtained  directly 
from  Fraulein  Letty  Oldberg,  in  Upsala,  Sweden, 
for  about  5  crowns  63  pfennigs.  Such  a  selection 
was  sent  me  by  Professor  Holmgren ;  and  similar 
ones  I  have  made  here,  and  used  in  my  testing. 
The  colors  of  the  green  and  purple  test  in  the  col- 
ored plate  in  the  Swedish,  French,  and  German 
editions  of  Professor  Holmgren's  book,  are  apt 
not  to  be  correct,  and  may  mislead  any  one. 
This  arises  from  the  difficulty  of  reproducing  in 
chromo-lithography  the  precise  tints,  and  render- 
ing these  permanent. 

To  learn  the  test,  I  would  strongly  advise,  not  a 
simple  perusal,  but  a  careful  and  repeated  study 


282  COLOR-BLINDNESS  : 

of  Holmgren's  directions  and  explanations  given 
in  this  volume.  Tliey  may  at  first  seem  rather  pro- 
lix; but  experience  will  soon  show  how  valuable 
his  minute  directions  are,  which,  when  properly 
studied,  will  relieve  many  a  doubt,  and  clear  up 
many  a  seeming  discrepancy  in  our  actual  test  of 
old  or  young.  When  thoroughly  understood  theo- 
retically, it  will  be  found  quite  simple,  and  readily 
adapted  to  test  even  very  young  children  with; 
as,  for  instance,  primary-school  children.  I  would 
advise  first  commencing  with  educated  adults,  and 
afterwards  testing  in  the  schools,  where  material 
is  more  at  hand  and  more  manageable.  We  shall, 
moreover,  meet  in  the  schools  of  lower  social  grade 
just  the  sort  of  stupidity  and  lack  of  appreciation 
which  we  are  likely  to  meet  among  uneducated 
railroad  employes,  sailors,  and  factory  workmen. 
It  is  a  curious  fact,  which,  I  think,  all  who  test 
large  numbers  will  sooner  or  later  find  out,  that 
dulness  of  comprehension  and  dulness  of  percep- 
tion will  almost  invariably  simulate  color-blindness. 
Many  a  teacher  in  our  schools  has  been  greatly  sur- 
prised that  I  have  not  marked  as  color-blind  a  boy 
who  seemed  to  them  to  do  about  the  same  as  the 
color-blind,  but  who  had  thrown  out  with  the  pat- 
tern a  single  worsted,  which  quickly  told  me  that 
I  had  to  deal  with  stupidity,  and  not  a  chromatic 
defect.  It  has  been  often  very  hard  to  disprove 
the  story  the  worsteds  picked  out  told,  when  that 
story  was  dictated  by  mental  dulness.  The  teach- 
ers generally  found  that  I  selected  their  brightest 
scholars  as  such. 

There  is  besides  this  a  dulness  of  color-percep- 
tion, or  rather  a  peculiar  slowness  in  the  colors 


ITS   DANGERS    AXD   ITS    DETECTIOX.  283 

taking  effect,  so  to  speak,  which  is  at  first  confus- 
ing to  the  examiner,  unless  he  bears  it  constantly 
in  mind,  and  is  familiar  with  it.  It  is  difficult  to 
describe,  but  is  yet  readily  recognized.  All  this 
adds  to  the  danger  of  our  considering  that  we  have 
at  least  partial  color-blindness  before  us,  and  hence 
increasing  our  ratio  at  the  expense  of  truth.  As 
inexperience  and  stupidity  will  most  trouble  us  in 
the  younger  classes  of  lowest  social  grades,  I 
would  advise  commencing  with  the  oldest  stu- 
dents one  can  avail  themselves  of,  and  then  going 
to  the  high  schools  before  the  grammar-schools. 
At  present  I  should  be  inclined  to  think,  that, 
however  seemingly  curious  and  interesting  it  might 
prove,  the  testing  for  color-blindness,  by  even  so 
simple  a  method  as  tliis  of  Holmgren's,  in  the  pri- 
mary schools,  would  be  time  lost,  as  well  as  likely 
to  mislead  one  as  to  the  relative  proportion,  &c. 
Moreover,  there  are  students  and  grammar-schol- 
ars enough  in  all  our  cities  of  any  size  to  furnish 
more  than  ample  material.  I  ought  to  add  here, 
however,  that  I  found  no  difficulty  with  the  sev- 
eral hundred  in  the  grammar-schools  who  had  just 
come  from  the  primary ;  i.e.,  witliin  a  few  days. 

All  my  examinations  were  made  with  Holm- 
gren's test.  My  purpose  was  to  quickly  obtain  an 
approximate  estimate  of  the  proportion  of  color- 
blind in  our  community,  and  at  the  same  time  to 
disseminate  a  knowledge  of  the  existence  of  such 
a  chromatic  defect  and  its  nature,  in  order  to  pre- 
pare the  way  for  some  action  in  reference  to  con- 
trol on  the  railroads  and  in  the  marine.  It  has 
been,  except  in  a  few  instances  of  educated  adults, 
wholly  impossible  for  me,  at  present,  to  test  those 


284  COLOE-BLDTDNESS  : 

I  found  color-blind  by  other  methods  than  Holm- 
gren's. My  own  experience,  however,  and  the 
reports  from  Europe  of  the  gentlemen  there  at 
work  in  this  investigation,  confirm  me  in  the 
belief,  that,  whatever  additional  method  I  might 
employ,  I  should  not  probably  change  my  opinion 
of  the  individual  case  of  color-blindness.  For  the 
purposes  I  have  had  in  view,  my  time  has  been 
better  spent  in  continued  work  in  our  schools, 
than  in  stopping  to  test  over  again,  by  additional 
methods,  persons  so  young  as  school-children  from 
eight  to  seventeen  years  of  age.  I  hope,  hereafter, 
to  accomplish  more  in  testing  the  adult  color-blind. 
For  a  time  I  worked  under  a  disadvantage  in 
reference  to  classifying  the  red  and  green  blind, 
because  my  purple  worsted  was  not  dark  enough, 
owing  to  the  color  having  faded  in  the  plate  in 
Holmgren's  book,  and  thereby  deceiving  me.  But 
I  supplemented  this  weak  point  in  my  decision  by 
having  a  red  and  a  green  worsted  of  as  nearly  as 
possible  the  same  degree  of  luminosity,  and  asking 
the  color-blind  which  was  the  darker.  Their  de- 
cision I  generally  found  very  quickly  made,  and 
adhered  to.  I  also  asked  them  to  pick  out  the 
hlaclc  worsteds,  and  found  they  would  select  the 
dark  greens  or  dark  reds,  according  as  they  were 
green  or  red  blind.  Since  I  have  had  the  proper 
shade  of  purple,  this  has  not  of  course  been  neces- 
sary. I  have,  however,  frequently  carried  it  out 
after  deciding  by  the  purple,  in  order  to  see  how 
accurate  my  previous  division  into  red  and  green 
probably  was.  I  have  decided  I  cannot  be  very 
far  from  right,  and  therefore  have  given  my 
records  as  I  made  them.     I  did  not  make  up  the 


ITS  DAKGEES  AND  ITS   DETECTIOK.  285 

tables  till  I  had  finished,  and  consequently  did  not 
know  what  the  relative  proportion  of  red  and 
green  blindness  was  during  the  time  I  was  testing. 
I  have  followed  Holmgren  in  making  three  di- 
visions,—  complete  red  and  green  blindness,  and 
partial  color-blindness.  My  three  cases  of  violet- 
blindness  I  have  allowed  to  stand  under  partial 
color-blindness.  These  I  have  found  the  test 
readily  showed.  As  color-blindness  exists  in  all 
degrees,  so  to  speak,  it  would  of  course  be  possi- 
ble, by  careful  special  examination  of  each  case,  to 
express  its  particular  degree ;  as  by  Donders's  meth- 
od or  by  Holmgren's  color-sense  tester.  The  per- 
centage of  color-blindness,  each  examiner  finds,  will 
be  modified  by  where  he  draws  the  line ;  that  is, 
how  feeble  must  the  chromatic  sense  be  to  come 
under  the  head  of  partial  color-blindness,  and  also 
what  shall  be  regarded  as  feeble  chromatic  sense, 
and  what  only  dulness  of  perception.  The  greater 
our  experience,  however,  the  more  carefully  can 
we  decide  these  points.  Holmgren's  method  with 
a  pretty  large  number  of  worsteds  has  seemed  to 
me  to  be  particularly  well  adapted  for  this  pur- 
pose. I  have  kept  to  the  original  plan  of  having 
a  large  number  of  green  worsteds,  finding  that  for 
my  purposes  it  worked  best ;  and  I  was  willing  to 
give  the  extra  time,  in  consideration  of  the  psy- 
chological study  it  afforded  me.  Professor  Holm- 
gren has  spoken  of  this.  I  am  not  certain  that 
with  young  people  it  is  not  best,  since  as  much 
time  is  wasted  by  their  searching  for  the  three  or 
four  greens  in  Holmgren's  modified  method,  as  in 
throwing  out  all  or  a  decisive  number  of  the 
greens  when  there  are  many  of  them.     I  think, 


286  COLOR-BLINDNESS : 

also,  it  gives  the  examiner  a  better  chance  to 
watch  the  play  of  the  hands,  from  which  so  much 
can  be  deduced. 

It  may  not  be  amiss  if  I  say  I  use  about  a  hun- 
dred and  fifty  skeins  of  worsted,  and  carry  them, 
wrapped  in  a  piece  of  white  cotton  cloth,  which  can 
be  spread  over  a  table  or  other  surface.  On  this  the 
colors  show  well  in  contrast.  When  statistics  are 
being  gathered,  or  large  numbers  must  be  tested 
with  the  smallest  loss  of  time,  this  plan  will  save 
trouble,  and  thereby  add  to  the  total  number  ex- 
amined. Even  amongst  the  youngest  scholars,  — 
and  several  hundred  were  just  from  the  primary 
schools,  —  I  have  not  failed  to  convince  myself, 
and  show  to  the  teachers,  color-blindness  where  it 
existed.  It  is  useless,  I  think,  to  argue  with  those 
of  my  European  friends  who  still  think  they  can 
always  detect  a  lack  of  chromatic  power  by  Stil- 
ling's  tables  or  other  method.  Their  number,  I  be- 
lieve, will  become  steadily  less  when  they  take  hold 
of  Holmgren's  test  in  earnest,  and  carry  it  out  as 
directed  by  him ;  as  has,  for  instance,  my  friend.  Dr. 
Magnus  of  Breslau.  My  experience  teaches  me  to 
advise  my  ophthalmic  brethren,  or  other  physicians 
who  will  be  called  upon  to  carry  out  the  work  I 
have  commenced  in  this  country,  to  waste  no  time 
with  other  methods,  but  to  fully  and  carefully 
familiarize  themselves  first  theoretically  with  Holm- 
gren's test,  and  then  practically  commencing  with 
adults. 


ITS   DANGERS   AND  ITS  DETECTION.         287 


CHAPTER   XXV. 

C0NCLX7SI0NS  AND  KECAPITULATION. 

One  male  in  twenty-five  is  color-blind  in  a  greater 
or  less  degree. 

Of  this  defect  they  may  even  themselves  be 
wholly  unconscious. 

This  blindness  is  red,  green,  or  violet  blindness. 
Total  color-blindness  also  occurs. 

This  defect  is  congenital.  It  exists  in  varying 
degrees.  It  is  largely  hereditary.  It  may  also  be 
temporarily  or  permanently  caused  by  disease  or 
injury. 

It  is  incurable  when  congenital.  Exercising  the 
eyes  with  colors,  and  the  ears  with  their  names, 
helps  the  color-blind  to  supplement  their  eyes,  but 
does  not  change  or  increase  their  color-perception. 

Experiment  and  experience  show  that  we  are 
forced  to  use  red  and  green  marine  signal-lights  to 
designate  a  vessel's  direction  of  motion  and  move- 
ments, and  at  least  red  lights  on  railways  to  desig- 
nate danger. 

Form,  instead  of  color,  cannot  be  used  for  these 
purposes. 

There  are  many  peculiar  conditions  under  which 


288  COLOR-BLINDNESS  : 

railroad  employes  and  mariners  perform  their  duty, 
which  render  colored  signals,  and  especially  colored 
lights,  difficult  to  be  correctly  seen. 

These  signals  can  never  be  correctly  seen  by  the 
color-blind.  There  are  such  among  railroad  em- 
ployes. 

There  is,  therefore,  great  danger  from  color- 
blindness. 

Railway  and  marine  accidents  have  occurred 
from  it. 

There  is  no  protection  but  the  elimination,  from 
the  personnel  of  railways  and  vessels,  of  all  per- 
sons whose  position  requires  perfect  color-percep- 
tion, and  who  fail  to  possess  this.  This  can  now 
be  readily  and  speedily  done. 

Therefore,  through  a  law  of  the  legislature, 
orders  from  state  railroad  commissioners,  or  by  the 
rules  and  regulations  of  the  railroad  corporations 
themselves,  each  and  every  employe  should  be 
carefully  tested  for  color-blindness  by  an  expert 
competent  to  detect  it.  The  test  and  the  method 
of  application  should  be  uniform.  All  deficient 
should  be  removed  from  their  posts  of  danger. 
Every  person  offering  himself  as  an  employ^  should 
be  tested  for  color-blindness,  and  refused  if  he  has 
it.  Every  employe  who  has  had  any  severe  illness, 
or  who  has  been  injured,  should  be  tested  again 
for  color-blindness  >efore  he  is  allowed  to  resume 
his  duties.  Periodic  examinations  of  the  whole 
personnel  should  alr^  be  required. 

Such  regulations  ire  generally  in  force  on  the 
European  railroads. 

An  international  (    amission  should  be  called  to 


ITS   DANGERS   AND   ITS   DETECTION.  289 

establish  rules  for  the  control  of  color-blindness 
on  the  sea,  and  the  carrying  out  the  same  exami- 
nations amongst  pilots,  masters,  and  crews  of 
steamers  and  sailing-vessels,  in  the  navies  and  the 
merchant  marine. 


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1  This  does  not  include,  except  incidentally,  vision  in  general,  or  simply 
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ophthalmic  Burgery,  are  omitted.  The  individual  titles  of  an  author's  articles 
are  not  always  given,  but  their  place  of  publication  follows  his  name. 

291 


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Archiv.  f.  Ophth.,  Bd.  xxv.,  Abth.  11.  — Benson,  W.  Man- 
ual of  the  Science  of  Color :  London,  1871. 

Cam.eron.  Color-Blindness  :  Edinburgh  Med.  Journal, 
Sept.,  1879.  —  Charpentier,  Dr.  A.  Arch.  Generales,  1878, 
July,  p.  118.  —  Colin,  H.  Sehscharfe  und  Farbensinn  bei 
electrischen  Lichte :  Centralblatt  f.  Augenh.,  April,  1879; 
Sehscharfe  und  Farbensinn  der  Nubier :  Centralblatt  f. 
Augenheil,  July,  1879 ;  Vergleichende  Messungen  der 
Sehscharfe  und  des  Farbensinns  bei  Tages-  Gas-  und  elec- 
trischenlichte :  Archiv.  f .  Augenheil,  vol  ,  viii.  1879  ;  Ueber 
quantitative  Farbensinn-Bestimmungen  bei  Europaern  und 
Nubiern :  Schles.  Gesellsch.  Sitzung,  Aug.  1,  1879  ;  Schle- 
sische  Zeitung,  Aug.  1,  1872.  Notiz  zur  Tabakamblyopie  : 
Centralblatt  f.  Augenheil,  Oct.,  1879.  Quantitative  Farben- 
Bestimmungen  :  Archiv.  f.  Ophth.,  vol.  ix.,  1879. —  Cours- 
serant.  Sur  I'emploi  methodique  des  verres  de  couleur  dans 
I'achromatopsie  :  Gaz  Med.,  No.  19, 1879.  —  Cintolesi,  Dr.  F. 
Intorno  alle  immagini  accidentali  o  soggettive :  Annali  di 
Ottalmologia,  Ann.  viii.  Fas.  2-3,  1879.  —  Chicago  Railway 
Review,  Aug.  30,  Sept.  13,  Oct.  4,  Oct.  25,  1879.— Cros. 
Les  Couleurs,  le  chromometre  et  la  photographic  des  couleurs : 
Journal  de  Physique,  1879,  vol.  viii. 


BIBLTOGEAPHY.  309 

Bonders,  F.  C.  Rapport  van  het  Gezichtsvermogen  van 
het  personeel  Staatspoorwegen :  Utrecht,  1879.  Also  in 
Report  Nederlandsche  Gasthuis  Oogligders,  1879.  —  Del- 
hoeuf.  Les  Sens  des  Couleurs  chez  les  Animaux :  Rev. 
Scient.,  May  24,  1879. 

Eder.  Ueber  die  cheraischen  Wirkung  des  farbigen 
Liclits  und  die  Photographie  in  naturlichen  Farben :  Wien, 
1879.  —  Edinburgh  Review.     Philosophy  of  Color,  Oct. ,  1 879. 

Pick.  Arch.  f.  Phys.,  vol.  xvii.,  1878.  — Fayre.  Gaz. 
Hebd. ,  12  S.,  xvi.  6,  7.  — Fontenay,  O.  E.  de.  Ueber  die 
Farbenblindheit  in  Danemark:  Centralblatt  f.  Augenheil, 
May,  1879,  p.  135. 

Gori,  T.  J.  J.  Ueber  Behandlung  von  Fehlern  in  der 
Farbenwahrnemung  :  Nederl.  Tijdsche  voor  Geneesk,  xiv., 
2  Afd.,  2  Aflev.,  p.  282.—  Gastchet,  Albert  S.  Adjectives 
of  Color  in  Indian  Languages  :  Am.  Naturalist,  Aug.,  1879. 

Hischberg,  J.  Ueber  eine  Modification  des  Spectroskops 
zur  Priifung  der  Farbenblinden :  Arch.  f.  Anat.  u.  Phys., 
Phys.  Abtheil,  Hef.,  1  u.  2,  p.  im.—HoscJi,  Fr.  Beitrag 
zur  Statistik  der  angeborenen  Farbenblindheit.  Correspon- 
denzbl.  f.  Schweiz.  Aerzte,  1879. — Holmgren.  Ueber  den 
Augenabstand  den  Farbeublinder:  Graefe's  Archiv.  f.Ophth., 
XXV.  i.,  1879 ;  A  Russian  translation  of  his  work  on  Color- 
Blindness,  1879 ;  Bidrag  till  Fargblindhetens  Statistik : 
Upsala,  1879,  pp.  136.  —  Hering.  Der  Lehre  von  Lichtsinn, 
2d  Aufl.  —  Hock.  Ueber  angeborene  Farbenblindheit : 
Wein.  Med.  Bl.,  1879,  ii.  566,  578,  QVd.—Hippel.  Ueber 
Farbenblindheit  :  Berl.  Klin.  Wochenschr.,  No.  39.  — 
Hcickel.  Origin  and  Development  of  the  Visual  Organs : 
Kosmos,  Nov.,  1878. — Harper's  Magazine,  Aug.,  1879,  p. 
^Ql.— Harper's  Weekly,  vol.  ii.,  1879,  p.  80Q.  — Helmholtz, 
H.  Popular  Lectures  on  Scientific  Subjects :  London, 
1873. 

Jeffries,  Dr.  B.  Joy.     Railway  Gazette,  N.  Y.  May  9, 1879. 

—  Just,  Dr.  0.     Statistik  der  Myopie  und  der  Farbensinnes. 

—  Kalischer.  Die  Gegenwart,  No.  32,  p.  93;  Farbenblind- 
heit :  Berlin,  1879.  —Kries,  Dr.  J.  Arch.  f.  Anat.  u.  Phys., 
1878.  —  Key.'^er,  P.  D.  Color-blind  R.R.  Employes  :  Penn. 
State  Med.  Soc,  May,  1879.  Treatment  of  Color-blindness 
by  Solution  of  Fuchsine :  Bost.  Med.  Jour.,  July  10,  1879. 

Lederer.      Zur  Mechanik  der  Farbenwahrnehmung,  Kos- 


810  BIBLIOGRAPHY. 

mos,  Mar.,  1879  :  Lancet,  Aug.  30, 1879.  —  Lloyd,  H.  Wave 
Theory  of  Light :  London,  1878. 

Magnus.  Ueber  methodische  Erziehung  des  Sinnesorgane, 
im  Besondereii  des  Farbensmnes:  Ausland,  No.  36,  1879. 
Farben-Tafel  zur  methodischen  Erziehung  des  Farben- 
sinnes  :  Breslau,  1879. — Moeller  (a  Mvelles).  Etude  crit- 
ique des  methodes  d'explorations  pour  les  recherches  des 
daltoniens  dans  le  personel  des  chemins  de  fer :  BulL  de 
I'Academie  r.  de  Med.de  Belg.,  1879,  xiii.,  2,  p.  283-330,  330- 
361.  —  Mcelles.  Du  Daltonisme  au  point  de  vue  theorique  et 
pratique :  Bruxelles,  H.  Ilanceaux,  1879.  —  Meyer.  Die 
relative  Helligkeit  der  Farben  ini  Sonnenlicht,  im  Gaslicht, 
und  im  Electrischenlicht :  Schlesische  Zeitung,  No.  356.  — 
Marty,  Dr.  Die  Frage  nach  der  geschichtlichen  Entwickel- 
ung  des  Farbensinnes :  Wien,  1879.  —  Maxwell,  J.  Clark. 
Theory  of  Comi:)ound  Colors  :  Phil.  Trans.  Roy.  Soc,  vol. 
cl.,  1860. 

Nuel.  (de  Louvain).  Des  Alterations  acquises  du  sens 
chromatique:  Annal.  d'Ocul.,  Jul. -Aug.  1879. 

Pole.  Nature,  Sept.  18,  1879.— P/wV/er,  Pro/.  Methoden 
zur  Untersuchung  auf  Farbenblindheit :  Gorrespondenz- 
Blatt.  f .  schweiz.  Aerzte,  Jahr.  ix.,  1879. 

Reuss,  Dr.  A.  Von.  Die  Farbenblindheit  in  ihrer  Bezie- 
hung  zu  den  Eisenbahnen,  insbesondere  Oesterreich-Un- 
garns :  Neue  Freie  Presse,  Sept.  4,  1879.  —  Railway  Review 
(Chicago).  Color-Blindness,  Aug.  30,  Sept.  13,  Oct.  4,  1879. 
Rood,  Ogden  N.     Modern  Chromatics,  1879. 

Stilling.  Die  Priifung  des  Farbensinnes  beim  Eisenbahn- 
und  Marine-Personal:  Allg.  Med.  Ztg.,  1879,  xxiv.,  293. 
—  Sully.  Harmony  of  Colors:  "Mind,"  No.  xiv.,  April, 
1879.  —  Stein.  Sehscharfe  und  Farbensinn  der  Nubier: 
Frankfurter  Zeitung,  No.  213,  l^Q.  —  Scliroeder,  Dr.  C. 
Die  Entwickelung  des  Farbensinnes  am  menschlichen  Auge : 
Berl.  Klin.  Wochenscher.,  No.  36,  I^IQ.  —  Scliadow.  Die 
Lichtsempfindlichkeit  der  peripheren  Netzhauttheile  in  Ver- 
haltniss  zu  dem  Raum-  und  Farbensinn  :  Arch.  f.  d.  ges. 
Phys.,  xix.  Heft  10,  11. 

Treitel,  Dr.  H.  Ueber  den  Werth  der  Gesichtsfeldmes- 
sung  mit  Pigmenten  f iir  die  Auffassung  der  Krankheiten  des 
nervosen  Sehapparates :  Graefe's  Archiv.,  Bd.  xxv.  Abth. 
ii.  and  iii.  —  Talko,  J.     Farbenblindheit :  Med.  Warszawa, 


BIBLIOGRAPHY.  311 

1879,  vii.,  p.  225-231.  Uutersuchung  der  Farbenblindheit 
beiin  Eisenbahn  Personal  :  Sowremennaja  ]\Iedicina,  No= 
11-12,  1879.  —  Tyndal,  J.  Six  Lectures  on  Light :  London, 
1873. 

VirchoiCy  R.  Farbensinne  der  Lapplander :  Bericht-  der 
Berlin  Gesells.  f.  Anthropologic,  Ethnologic,  und  Urge- 
schichte :  Sitzung  15,  Mar.  1879,  p.  64. 

Wolfe,  Dr.  J.  R.  Med.  Times  and  Gazette,  Apr.  19, 
Aug.  2,  1879.  —  Weher,  Ad.  Apparat  zur  numerischen 
Priifung  des  Farbensinnes  :  Klin.  Monatsbl.  f .  Augenheil, 
xvi.,  p.  130. 


INDEX. 


A. 

Page 
Accidents  cause  color-blindness,    49 
Accidents  on  the  ocean       .        .  161 
Admiral,  British  service,  color- 
blind        14 

Alcohol  causes  color-blindness  .  49 
Allen  Grant,  color-sense  .  ._  91 
American  statistics  .  68,  75,  78 
Automatic  color-signals  .  .  20 
Applicants  for  railroad  service, 

testing 232 

Army,  control  in .  .  •  •  177 
Army,  U.S.,  soldiers  color-blind,  78 
Aubert,  idea  of  color-blindness,    65 


B. 

Babbage's  account  of  Dalton  .  8 
Blank  forms  for  tests  .  .  .261 
Blind,  the,  use  of  color  names,  97,  98 
Blind,  the,  using  other  senses  .  122 
Blindness,  red,  green,  violet  .  30 
Blindness,  total,  for  color  .  .  35 
Board  of  Health,  Mass.,  Report,  80 
Burnett,  Dr.  S.  M.,  color-blind 
negroes 68 


Cohn  on  heredity         .        .       .61 

Cohn's  test 194 

Cohn's  use  of  contrast .        .        .  189 
Cohn's  chromasciopticon    .        .  189 
Collisions  on  the  sea    .        .        .161 
Color-blind,  color-sense  of .        .    47 
Condition  of  vision  of       .        .    43 
Engineer    ....   152,  153 
Former    classification    of,    by 
Seebeck,    Szokalski,    Purk- 
inje,  and  Wartman        .       22-25 
Precise  condition  of  vision  of,    43 
Present    classification    by 
Young-Hehnholtz  theory,   26-41 


Page 
Color-blind,  railroad  employes, 

how  they  escape  danger  153-160 
Their  relation  to  railroad  sig- 
nals   150 

Sea-captain        .        .        .        .52 
Color-blindness,  accidents  from 
on  ocean         ....  161 
Dangers  from,  on  land      .        .  137 
Dangers  from,  on  ocean  .        •  161 
Frequency  among  railroad  em- 
ployes      142 

No  control  of,  in  United  States,  176 
Not  discussed  by  press  .  .  138 
Concealment  of.  .  88-110-237 
Curability  of,  Favre  .        .  Ill 

Physical  peculiarities  of,  Cohn, 

Magnus,  Pfliiger,  Holmgren  •    65 
Frequency  in  males .        .        69-79 
From  disease  and  injury, Favre, 
Wilson,  Hays,  Cooper,  Wal- 
ton          49-52 

Hereditary,  Earle,  Dalton, 
Cunier,  Hochecher,  Wilson, 
Horner,  Cohn,  Magnus,  54-63 
Hereditary  in  females  .  .  57 
In  colored  race  .  .  .  .68 
In  European  women  .  .  85 
In  school-girls  .  .  .  .87 
IncurabiUty  of  .  .  Ill,  123-124 
Palliation  of  .  .  .  .125 
Palliation  of,  by  colored  glass,  126 
PaUiation  by  colored  fluids,  129-136 
Palliation  of,    by  night    fight 

128-129 

Infrequency  in  females     .        80-87 

Violet  bfindness        •        .       77,  79 

Color-names .        .        .        .       90,  97 

By  the  blind      .        .        .      97-100 

In  schools 123 

Colquhoun's,  Dr.,  case        .        .      9 
Cunard  Steamship  Co.          .        .  258 
Cunier,  cases  of  color-bfind  fe- 
males       56 

313 


314 


INDEX. 


Dajie,  Dr.,  color-blindness  on  the 

ocean 165 

Per  cent,  Norway     .        .        .73 

Daae's  test 194 

Dalton's  case         ...       4,  117 

per  cent 69 

Dangers  from  color-blindness     .  137 
Delboeuf  and  Spring,  palliation  of 

color-biindness  .  .  .  129 
Disease  causing  color-blindness,  50 
Difficulty  of  control  in  U.  S.  .  176 
Donders's  method,  191,  195,  246-250 
Dor,  Dr.  H.,  per  cent  .  .  .81 
Dor  and  Favre's  test  .  .  .  191 
Dove's  per  cent    .        .        .        .70 

E. 

Earle,  Dr.  Pliny's  family     .        .    54 
Employes,  railway,  color-blind, 

142-147 
Railway,  color-blind,  condition 

of 148-153 

Railway,  already  in  service     .  233 
Railway,  already    in  service, 

testing 232 

Engineer,  color-blind,     152,  153,  160 
Engraver,  color-blind  .        .        .13 


Favre,  Dr.,  color-blind  sailors    .  163 

Cure  of  color-blindness    .    111-114 

Report  of  Lyons  Railroad        .  260 

Females  rarely  color-blind .       85,  87 

Feris,  Dr.,  color-blind  sailors     ,  163 

Per  cent 72 

Feigning  color-blindness  .  .  237 
Fick's  theory  .  .  .  .198 
Finland,  color-blindness  in  .  146 
Fog,  effect  of,  on  colors  .  .  162 
Fontenoy,  Dr.,  per  cent  .  .  73 
Forbes,  effect  of  steam  .  .154 
Form  for  color  in  signals  .  .  171 
Forster's  perimeter  .  .  .  197 
Fuchsine,  solution  of,  to  palliate 
color-blindness      .        .        .  130 


Gallet,  Lieut.,  per  cent       .        .    72 
Git,  M.,  per  cent  ....     71 
Gintl,  Dr.,  report 
Goubert,  Dr.,  treatment  of  color 

blindness        ... 
Gould,  Dr.  B.  A.,  color-blind 

ness  in  U.  S.  soldiers    .        .     72 
Guillot,  per  cent  .        .        .        .72 

n. 

flandelministeriura  of  Austria   .  277 

of  I'russia 265 

iLirris  case,  Huddart's  account 
of 2 


Hays,  Dr.,  case  of  color-blind- 
ness          50 

Herschel,  Sir  John,  remai'ks  on 

Mr.  Pole's  case       .        .        .46 
Helmholtz,  Prof.,  use  of  names  in 

test 115 

Theory  of  color-sense  .  .  26 
Hirschberg's  spectroscope  .  .  190 
Hochecher,  Dr.,  color-blind  fam- 

ily 57 

Holmgren's  experience  with  col- 
or-blind employes  .        .  145 
Holmgren,   Prof.,  Young-Helm- 
holtz  theory   .        .        .        .26 
Criticism  of  Dr.  Favre     .        .  121 
On  change  of  signals        .    167-174 
Color-blindness  among  females,   82 
Color-names       .        .        .        .94 
Holmgren  on  methods  of  testing, 

183-188,  196,  201-219 
Holmgren's  chromatoskiameter,  241 
Special  directions  for  testing, 

221-231 

Former  publications         .    196-200 

Measurement  of  color-blind    .    66 

Horner's  law  of  heredity     .        .    58 

Cases 59,  60 


I. 

Incurability  of  coloi'-blindness    .  Ill 
Infrequency  of  color-blindness  in 

females 80 

International  commission    .  165,  288 


Javal,  criticism  of  Delboeuf  .  136 
Jeffries,  per  cent  .  .  74,  75,  87 
Jews  color-blind  .        .        .       58-76 

K. 

Kelland,  Prof.,  per  cent  .  .  69 
Krohn,  Dr.,  per  cent,  Finland,  73-146 

L. 

Laws  of  control  on  railroads  in 

Europe 251 

Sweden      ....    252-254 

Norway 257 

Bavaria 258 

Italy 259 

Belgium 259 

Holland 261 

England     ....    263-265 
Prussia 265 

Laws  of   control    in    navies  of 

Europe 255 

Sweden       ....    255-257 

Norway 257 

France 258 

Holland 262 

Austria 163 

Lederer,  Dr.,  report  on  color- 
blind sailors  ....  163 


IKDEX. 


315 


Light  and  shade,  value  of,  to  col- 
or-blind   104 


M. 

Magnus  on  heredity  .  .  .  61 
Criticism  of  German  railroads,  266 
Massachusetts,  action  of  .  .  178 
Railroad  Commissioners,  138,  279 
Maxwell's  color  top  .  .  .  192 
Marine    signals,    can    they    be 

changed?  .  .  .  .166 
Merchant  marine  ....  177 
Metliods  of  testing  .  .  .182 
Meyer's  law  of  contrast  .  .  189 
Minder,  Dr.,  per  cent  .        .        .74 

Employes 152 

Mistakes  of  color-bUnd        .        .      7 
Wilson's  reports  of  .        .       10-14 
Author's  reports  of  .        .       17-21 
Mixture  of  red  and  green  lights 

makes  white  ....  158 
Moui-and,  per  cent       .        .        .72 


Navy,  control  in  . 

Holland      .... 

France       .... 

Noi-way     .... 

Sweden      .... 

Denmark   .... 

Austria       .... 
Negi'oes  color-blind     . 
Nelson,  Mr.  Thomas,  notes  on 

color-blindness 
Niemetscheck,    idea    of    color- 
blindness 

Disproved    by  Cohn,  Pfliiger, 

Holmgren       ...       6 

Nicholl,  Dr.,  cases        .         5,  6, 

NickoU,  helm-signals  . 

Nickel,  chloride  of,  causes  color 

blindness 
Noel  warns  as  to  color-blindness 
Number  for  color  in  signals 


177 

262 
258 
257 
255 
163 
163 


,10 


131 
141 
172 


P. 

Parliament,  no  action  of  .  .  265 
Peculiar  look  of  color-blind  .  67 
Perkins  Institution  for  the  Blind, 

test  of  coloi'-names  in    .        .96 
Pfliiger's  measurements  pf  color- 
blind        67 

Use  of  contrast .  .  .  .189 
Physicians  color-blind  .  17-19 
Pole,  Mr.,  account  of  his  own 

case 43 

Post-office  clerk  color-blind  .  21 
Practical  life,  color-blindness  in,  88 
Prevost,  per  cent .  .  .  .69 
Prior  on  color-names  .  .  .90 
Power,  Dr.  H.,  case     .        .        .109 


Q. 

Quaghno,  Dr.,  color-bUndness  in 

Italy 143 

Quantitative  determination,    241-246 
Quakers,  color-bhnd    .        .        .16 


Railroad  Commissioners'  report 

on  color-bhndness  .        .  133 

Railroads  in  United  States  not 

protected  ....  176 
Railroad  signals,    can    they    be 

changed?  ....  166 
Raih'oad  employes  color-blind, 

142-146 

Perception  of  color-blind        .  148 

Raynaud,  effect  of  fog         .        .  162 

Relationship  of  color-blind         .     66 

Remedy,    supposed,   for    color- 

bU'idness  ....  133 
Recapitulation  ....  286 
Reuss,  Dr.,  per  cent  .  .  .  143 
Romberg,  marine  accidents  .  161 
Rose's  color-measurer  .  .  190 
Rowe,  Dr.,  per  cent     .        .        .69 


S. 

Sailors  color-blind        .        .        .  163 
Sanitary  Commission,  U.S.  test 

of  color-blind  .  .  .78 
School-girls  color-blind  .  85-87 
School-boys  color-bhnd  .  74-75 
Schools,  teaching  colors  in  .  .  123 
Scotch  railroad,  tests  on  .  .  264 
Schirmer's  use  of  contrast  .  •  190 
Scott,  Mr.  J.,  his  own  case  .  .  4 
Seebeck,  Prof.,  classification  of 
color-blmd      .        .        .        .23 

Test 192 

Sea  captains,  color-bhnd  .  .  52 
Signals,  marine  and  railroad,  can- 
not be  changed  .  .  .  166 
Spectrum  shortened  at  violet  end,  79 
Steebach's  colored  glasses  .  .  126 
Steam  changes  colors  .  .  .  154 
StiUing,    Prof.,    warning    as  to 

tests 100 

Per  cent 73 

Use  of  shadows         .        .        .  188 

Test 191 

Surgeons,  English  railroad .        .  264 
Sweden,  color-bUndness  on  rail- 
roads of 179 

Szokalski,  classification  of  color- 
blind        24 


Teaching  colors  in  schools  .  .  123 
Tobacco  causes  color-bhndness,  50 
Total  color-bhndness  .  .  .35 
Tuberville's,  Dr.,  case  .  .  1 
Tyndal  red  and  green  lights        .  158 


316 


INDEX. 


United  States  Railroad  signals   .  175 


Ville  du  Havre,  loss  of,  attributed 

to  color-blindness  .        .        .  164 

Visual  field,  colors  in  .        .        .37 

Color-zones  of  .        .        .        .38 

Vineyard-Haven  lights        .        .    20 

W. 

Walton's  case  of  color-blind  en- 
gineer      62 


"Wartman,  Prof.  Elie,  classifica- 
tion          25 

Palliation  of  color-blindness  .  126 
Weber's  use  of  contrast  .  .  189 
Wbewell's  account  of  Dalton  .  8 
Wilson's  tests  .  .  .  .193 
Woinow's  test  ....  192 
Women,  color-blind    .        .        .56 


T. 

Young-Helmholtz  theory   .       .    28 


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